The last reason why get_cpu_idle/iowait_time_us() may return -1 now is if
the config doesn't support nohz.
The ad-hoc replacement solution by cpufreq is to compute jiffies minus the
whole busy cputime. Although the intention should provide a coherent low
resolution estimation of the idle and iowait time, the implementation is
buggy because jiffies don't start at 0.
Just provide instead a real get_cpu_[idle|iowait]_time_us() offcase.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-14-frederic@kernel.org
Fetching the idle cputime is available through a variety of accessors all
over the place depending on the different accounting flavours and needs:
- idle vtime generic accounting can be accessed by kcpustat_field(),
kcpustat_cpu_fetch(), get_idle/iowait_time() and
get_cpu_idle/iowait_time_us()
- dynticks-idle accounting can only be accessed by get_idle/iowait_time()
or get_cpu_idle/iowait_time_us()
- CONFIG_NO_HZ_COMMON=n idle accounting can be accessed by kcpustat_field()
kcpustat_cpu_fetch(), or get_idle/iowait_time() but not by
get_cpu_idle/iowait_time_us()
Moreover get_idle/iowait_time() relies on get_cpu_idle/iowait_time_us()
with a non-sensical conversion to microseconds and back to nanoseconds on
the way.
Start consolidating the APIs with removing get_idle/iowait_time() and make
kcpustat_field() and kcpustat_cpu_fetch() work for all cases.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-13-frederic@kernel.org
Although the dynticks-idle cputime accounting is necessarily tied to the
tick subsystem, the actual related accounting code has no business residing
there and should be part of the scheduler cputime code.
Move away the relevant pieces and state machine to where they belong.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-10-frederic@kernel.org
The non-vtime dynticks-idle cputime accounting is a big mess that
accumulates within two concurrent statistics, each having their own
shortcomings:
* The accounting for online CPUs which is based on the delta between
tick_nohz_start_idle() and tick_nohz_stop_idle().
Pros:
- Works when the tick is off
- Has nsecs granularity
Cons:
- Account idle steal time but doesn't substract it from idle
cputime.
- Assumes CONFIG_IRQ_TIME_ACCOUNTING by not accounting IRQs but
the IRQ time is simply ignored when
CONFIG_IRQ_TIME_ACCOUNTING=n
- The windows between 1) idle task scheduling and the first call
to tick_nohz_start_idle() and 2) idle task between the last
tick_nohz_stop_idle() and the rest of the idle time are
blindspots wrt. cputime accounting (though mostly insignificant
amount)
- Relies on private fields outside of kernel stats, with specific
accessors.
* The accounting for offline CPUs which is based on ticks and the
jiffies delta during which the tick was stopped.
Pros:
- Handles steal time correctly
- Handle CONFIG_IRQ_TIME_ACCOUNTING=y and
CONFIG_IRQ_TIME_ACCOUNTING=n correctly.
- Handles the whole idle task
- Accounts directly to kernel stats, without midlayer accumulator.
Cons:
- Doesn't elapse when the tick is off, which doesn't make it
suitable for online CPUs.
- Has TICK_NSEC granularity (jiffies)
- Needs to track the dyntick-idle ticks that were accounted and
substract them from the total jiffies time spent while the tick
was stopped. This is an ugly workaround.
Having two different accounting for a single context is not the only
problem: since those accountings are of different natures, it is
possible to observe the global idle time going backward after a CPU goes
offline.
Clean up the situation with introducing a hybrid approach that stays
coherent and works for both online and offline CPUs:
* Tick based or native vtime accounting operate before the idle loop
is entered and resume once the idle loop prepares to exit.
* When the idle loop starts, switch to dynticks-idle accounting as is
done currently, except that the statistics accumulate directly to the
relevant kernel stat fields.
* Private dyntick cputime accounting fields are removed.
* Works on both online and offline case.
Further improvement will include:
* Only switch to dynticks-idle cputime accounting when the tick actually
goes in dynticks mode.
* Handle CONFIG_IRQ_TIME_ACCOUNTING=n correctly such that the
dynticks-idle accounting still elapses while on IRQs.
* Correctly substract idle steal cputime from idle time
Reported-by: Xin Zhao <jackzxcui1989@163.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-8-frederic@kernel.org
Currently whether generic vtime is running or not, the idle cputime is
fetched from the nohz accounting.
However generic vtime already does its own idle cputime accounting. Only
the kernel stat accessors are not plugged to support it.
Read the idle generic vtime cputime when it's running, this will allow to
later more clearly split nohz and vtime cputime accounting.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-5-frederic@kernel.org
The first parameter to kcpustat_field() is a pointer to the cpu kcpustat to
be fetched from. This parameter is error prone because a copy to a kcpustat
could be passed by accident instead of the original one. Also the kcpustat
structure can already be retrieved with the help of the mandatory CPU
argument.
Remove the needless parameter.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-4-frederic@kernel.org
Offline handling happens from within the inner idle loop, after the
beginning of dyntick cputime accounting, nohz idle load balancing and
TIF_NEED_RESCHED polling.
This is not necessary and even buggy because:
* There is no dyntick handling to do. And calling tick_nohz_idle_enter()
messes up with the struct tick_sched reset that was performed on
tick_sched_timer_dying().
* There is no nohz idle balancing to do.
* Polling on TIF_RESCHED is irrelevant at this stage, there are no more
tasks allowed to run.
* No need to check if need_resched() before offline handling since
stop_machine is done and all per-cpu kthread should be done with
their job.
Therefore move the offline handling at the beginning of the idle loop.
This will also ease the idle cputime unification later by not elapsing
idle time while offline through the call to:
tick_nohz_idle_enter() -> tick_nohz_start_idle()
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20260508131647.43868-3-frederic@kernel.org
When the nohz idle time is fetched, the current clock timestamp is taken
outside the seqcount, which can result in a race as reported by Sashiko:
get_cpu_sleep_time_us() tick_nohz_start_idle()
----------------------- ---------------------
now = ktime_get()
write_seqcount_begin(idle_sleeptime_seq);
idle_entrytime = ktime_get()
tick_sched_flag_set(ts, TS_FLAG_IDLE_ACTIVE);
write_seqcount_end(&ts->idle_sleeptime_seq);
read_seqcount_begin(idle_sleeptime_seq)
delta = now - idle_entrytime);
//!! But now < idle_entrytime
idle = *sleeptime + delta;
read_seqcount_retry(&ts->idle_sleeptime_seq, seq)
Here the read side fetches the timestamp before the write side and its
update. As a result the time delta computed on the read side is negative
(ktime_t is signed) and breaks the cputime monotonicity guarantee.
This could possibly be fixed with reading the current clock timestamp
inside the seqcount but the reader overhead might then increase. Also
simply checking that the current timestamp is above the idle entry time
is enough to prevent any issue of the like.
Fixes: 620a30fa0b ("timers/nohz: Protect idle/iowait sleep time under seqcount")
Reported-by: Sashiko
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260508131647.43868-2-frederic@kernel.org
The validation check uses '>' instead of '>=' when comparing tv_usec
against USEC_PER_SEC, allowing the value 1000000 through. After
conversion to nanoseconds (*= 1000), this produces tv_nsec ==
NSEC_PER_SEC, violating the timespec invariant that tv_nsec must be
less than NSEC_PER_SEC.
Use '>=' to reject tv_usec values that are not in the valid range of
0 to 999999.
Fixes: 5e0fb1b57b ("y2038: time: avoid timespec usage in settimeofday()")
Signed-off-by: Naveen Kumar Chaudhary <naveen.osdev@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/4rikk44zew3s6577dugmx4jyblz7o5c57niuap6ct3td5yfm6w@gh7pcumg7qor
The stub for arch_inlined_clockevent_set_next_coupled() has 'u64 u64
cycles' in its parameter list. Since u64 is a typedef, the compiler
parses the second 'u64' as the parameter name, making 'cycles' an
unused token. Remove the duplicate so the parameter is correctly named.
Fixes: 89f951a1e8 ("clockevents: Provide support for clocksource coupled comparators")
Signed-off-by: Naveen Kumar Chaudhary <naveen.osdev@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/7tostpvxzdn6tobmyow63a5rweatls5kux3scqp2vzhe7mv6uq@ecr746b4hyhf
timens_ktime_to_host() in compares the current time namespace against
init_time_ns for the fast path. It calls do_timens_ktime_to_host() for the
offset case. Both symbols are needed at link time by any caller of the
inline.
All current callers are builtin, but ntsync can be built as module, which
prevents it from using it.
Export both with EXPORT_SYMBOL_GPL.
Signed-off-by: Maoyi Xie <maoyixie.tju@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Link: https://patch.msgid.link/20260528063311.3300393-2-maoyixie.tju@gmail.com
When CONFIG_UBSAN_ALIGNMENT is enabled, the stack usage of nocb_gp_wait()
grows above typical warning limits:
In file included from kernel/rcu/tree.c:4930:
kernel/rcu/tree_nocb.h: In function 'rcu_nocb_gp_kthread':
kernel/rcu/tree_nocb.h:866:1: error: the frame size of 1968 bytes is larger than 1280 bytes [-Werror=frame-larger-than=]
Apparently, the problem is passing rcu_data from a 'void *' pointer,
which gcc assumes may be misaligned. When the function is not inlined
into rcu_nocb_gp_kthread(), that is no longer visible to gcc.
Add a 'noinline_for_stack' annotation that leads to skipping a lot of
the alignment sanitizer checks and keeps the stack usage 60% lower here.
Reviewed-by: Kunwu Chan <chentao@kylinos.cn>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Add syntax to the parsing of eprobes to be able to typecast a trace event
field that is a pointer to a structure.
Currently, a dereference must be a number, where the user has to figure
out manually the offset of a member of a structure that they want to
dereference.
But for event probes that records a field that happens to be a pointer to
a structure, it cannot dereference these values with BTF naming, but
must use numerical offsets.
For example, to find out what device a sk_buff is pointing to in the
net_dev_xmit trace event, one must first use gdb to find the offsets of the
members of the structures:
(gdb) p &((struct sk_buff *)0)->dev
$1 = (struct net_device **) 0x10
(gdb) p &((struct net_device *)0)->name
$2 = (char (*)[16]) 0x118
And then use the raw numbers to dereference:
# echo 'e:xmit net.net_dev_xmit +0x118(+0x10($skbaddr)):string' >> dynamic_events
If BTF is in the kernel, then instead, the skbaddr can be typecast to
sk_buff and use the normal dereference logic.
# echo 'e:xmit net.net_dev_xmit (sk_buff)skbaddr->dev->name:string' >> dynamic_events
# echo 1 > events/eprobes/xmit/enable
# cat trace
[..]
sshd-session-1022 [000] b..2. 860.249343: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.250061: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.250142: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.263553: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.283820: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.302716: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.322905: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.342828: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.362268: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.382335: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.400856: xmit: (net.net_dev_xmit) arg1="enp7s0"
sshd-session-1022 [000] b..2. 860.419893: xmit: (net.net_dev_xmit) arg1="enp7s0"
The syntax is simply: (STRUCT)(FIELD)->MEMBER[->MEMBER..]
Also add comments around the #else and #endif of #ifdef CONFIG_PROBE_EVENTS_BTF_ARGS
to know what they are for.
Link: https://lore.kernel.org/all/20260601130746.2139d926@gandalf.local.home/
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
assign_cfs_rq_runtime() during update_curr() sets the resched indicator
and relies on check_cfs_rq_runtime() during pick_next_task() /
put_prev_entity() to throttle the hierarchy once current task is
preempted / blocks.
Per-task throttle, on the other hand, uses throttle_cfs_rq() to simply
propagate the throttle signals, and then relies on task work to
individually throttle the runnable tasks on their way out to the
userspace.
Remove check_cfs_rq_runtime() and unify throttling into
account_cfs_rq_runtime() which only sets the cfs_rq->throttled,
cfs_rq->throttle_count indicators via throttle_cfs_rq() and optionally
adds the task work to the current task (donor) it is on the throttled
hierarchy.
throttle_cfs_rq() requests for sched_cfs_bandwidth_slice() worth of
bandwidth for the current hierarchy that enable it to continue running
uninterrupted when selected. For the rest, it requests a bare minimum of
"1" to ensure some bandwidth is available and pass the
"runtime_remaining > 0" checks once selected.
For SCHED_PROXY_EXEC, a mutex holder cannot exit to userspace without
dropping it first and the mutex_unlock() ensures proxy is stopped before
the mutex handoff which preserves the current semantics for running a
throttled task until it exits to the userspace even if it acts as a
donor.
[ prateek: rebased on tip, comments, commit message. ]
Reviewed-By: Benjamin Segall <bsegall@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260602071005.11942-1-kprateek.nayak@amd.com
An update_curr() during the enqueue of throttled task will start
throttling the hierarchy from subsequent commit. This can lead to
tg_throttle_down() seeing non-empty throttled_limbo_list for the cfs_rq
attaching the task from throttled_limbo_list one by one. For example:
R
|
A
/ \
*B C
|
rq->curr
*B is throttled with tasks on hte limbo list. When the tasks are
unthrottled via tg_unthrottle_up() and entity of group B is placed onto
A, update_curr() is called to catch up the vruntime and it may throttle
group A causing the subsequent tg_throttle_down() to see the pending
task's on B's limbo list.
tg_unthrottle_up()
/* --cfs_rq->throttle_count == 0 */
list_for_each_entry_safe(p, cfs_rq->throttled_limbo_list)
enqueue_task_fair()
enqueue_entity(se /* B->se */)
update_curr(cfs_rq /* A->gcfs_rq */)
account_cfs_rq_runtime(cfs_rq)
throttle_cfs_rq(cfs_rq /* A->gcfs_rq */ )
tg_throttle_down()
/* Reaches B->cfs_rq with throttle_count == 0 */
!!! !list_empty(&cfs_rq->throttled_limbo_list)) !!!
Move the tasks from throttled_limbo_list onto a local list before
starting the unthrottle to prevent the splat described above. If the
hierarchy is throttled again in middle of an unthrottle, put the pending
tasks back onto the limbo list to prevent running them unnecessarily.
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Benjamin Segall <bsegall@google.com>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260602052531.11450-2-kprateek.nayak@amd.com
Subsequent commits will allow update_curr() to throttle the hierarchy
when the runtime accounting exceeds allocated quota. Call update_curr()
before the unthrottle event, and in tg_unthrottle_up() to catch up on
any remaining runtime and stabilize the "runtime_remaining" and
"throttle_count" for that cfs_rq.
Doing an update_curr() early ensures the cfs_rq is not throttled right
back up again when the unthrottle is in progress.
Since all callers of unthrottle_cfs_rq(), except two, already update the
rq_clock and call rq_clock_start_loop_update(), move the
update_rq_clock() from unthrottle_cfs_rq() to the callers that don't
update the rq_clock.
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Benjamin Segall <bsegall@google.com>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260602052531.11450-1-kprateek.nayak@amd.com
When distribute_cfs_runtime() encounters a local cfs_rq, it adds it to a
local list and unthrottles it at the end, when it is done unthrottling
other cfs_rq(s) on cfs_b->throttled_cfs_rq until the bandwidth runs out.
Instead of using a local list, reuse the local CPU's
rq->throttled_csd_list and the __cfsb_csd_unthrottle() path for
unthrottle.
If this is the first cfs_rq to be queued on the "throttled_csd_list", it
prevents the need for a remote CPUs to interrupt this local CPU if they
themselves are performing async unthrottle.
If this is not the first cfs_rq on the list, there is an async unthrottle
operation pending on this local CPU and the unthrottle can be batched
together.
No functional changes intended.
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Benjamin Segall <bsegall@google.com>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260602050005.11160-3-kprateek.nayak@amd.com
Routine conversion of rcu_read_lock(), spin_lock*, and rq_lock usage
within the cfs bandwidth controller to use class guards.
Only notable changes are:
- Checking for "cfs_rq->runtime_remaining <= 0" instead of the inverse
to spot a throttle and break early. This also saves the need
for extra indentation in the unthrottle case.
- Reordering of list_del_rcu() against throttled_clock indicator update
in unthrottle_cfs_rq(). Both are done with "cfs_b->lock" held after
the "cfs_rq->throttled" is cleared which make the reordering safe
against concurrent list modifications.
No functional changes intended.
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ben Segall <bsegall@google.com>
Tested-by: Aaron Lu <ziqianlu@bytedance.com>
Link: https://patch.msgid.link/20260602050005.11160-2-kprateek.nayak@amd.com
To remove the cfs_rq pointer array in task_group, allocate the combined
cfs_rq and sched_entity using the per-cpu allocator.
This patch implements the following:
- Changes task_group->cfs_rq from 'struct cfs_rq **' to
'struct cfs_rq __percpu *'.
- Updates memory allocation in alloc_fair_sched_group() and
free_fair_sched_group() to use alloc_percpu() and free_percpu()
respectively.
- Uses the inline accessor tg_cfs_rq(tg, cpu) with per_cpu_ptr() to retrieve
the pointer to cfs_rq for the given task group and CPU.
- Replaces direct accesses tg->cfs_rq[cpu] with calls to the new tg_cfs_rq(tg,
cpu) helper.
- Handles the root_task_group: since struct rq is already a per-cpu variable
(runqueues), its embedded cfs_rq (rq->cfs) is also per-cpu. Therefore, we
assign root_task_group.cfs_rq = &runqueues.cfs.
- Cleanup the code in initializing the root task group.
This change places each CPU's cfs_rq and sched_entity in its local per-cpu
memory area to remove the per-task_group pointer arrays.
Signed-off-by: Zecheng Li <zecheng@google.com>
Signed-off-by: Zecheng Li <zli94@ncsu.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Josh Don <joshdon@google.com>
Link: https://patch.msgid.link/20260522141623.600235-4-zli94@ncsu.edu
Now that struct sched_entity is co-located with struct cfs_rq for non-root task
groups, the task_group->se pointer array is redundant. The associated
sched_entity can be loaded directly from the cfs_rq.
This patch performs the access conversion with the helpers:
- is_root_task_group(tg): checks if a task group is the root task group. It
compares the task group's address with the global root_task_group variable.
- tg_se(tg, cpu): retrieves the cfs_rq and returns the address of the
co-located se. This function checks if tg is the root task group to ensure
behaving the same of previous tg->se[cpu]. Replaces all accesses that use
the tg->se[cpu] pointer array with calls to the new tg_se(tg, cpu) accessor.
- cfs_rq_se(cfs_rq): simplifies access paths like cfs_rq->tg->se[...] to use
the co-located sched_entity. This function also checks if tg is the root
task group to ensure same behavior.
Since tg_se is not in very hot code paths, and the branch is a register
comparison with an immediate value (`&root_task_group`), the performance impact
is expected to be negligible.
Signed-off-by: Zecheng Li <zecheng@google.com>
Signed-off-by: Zecheng Li <zli94@ncsu.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Josh Don <joshdon@google.com>
Link: https://patch.msgid.link/20260522141623.600235-3-zli94@ncsu.edu
Improve data locality and reduce pointer chasing by allocating struct
cfs_rq and struct sched_entity together for non-root task groups. This
is achieved by introducing a new combined struct cfs_tg_state that
holds both objects in a single allocation.
This patch:
- Introduces struct cfs_tg_state that embeds cfs_rq, sched_entity, and
sched_statistics together in a single structure.
- Updates __schedstats_from_se() in stats.h to use cfs_tg_state for accessing
sched_statistics from a group sched_entity.
- Modifies alloc_fair_sched_group() and free_fair_sched_group() to allocate
and free the new struct as a single unit.
- Modifies the per-CPU pointers in task_group->se and task_group->cfs_rq to
point to the members in the new combined structure.
Signed-off-by: Zecheng Li <zecheng@google.com>
Signed-off-by: Zecheng Li <zli94@ncsu.edu>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: K Prateek Nayak <kprateek.nayak@amd.com>
Reviewed-by: Josh Don <joshdon@google.com>
Link: https://patch.msgid.link/20260522141623.600235-2-zli94@ncsu.edu
Commit ed4fb6d7ef ("hrtimer: Use and report correct timerslack values
for realtime tasks") sets timer_slack_ns to 0 for RT tasks in
__setscheduler_params(). However, when an RT task with SCHED_RESET_ON_FORK
creates child threads, the children inherit timer_slack_ns=0 from the
parent. sched_fork() resets the child's policy to SCHED_NORMAL but does
not restore timer_slack_ns, leaving the child permanently running with
zero slack.
Fix this by restoring timer_slack_ns from default_timer_slack_ns in
sched_fork() when resetting from RT/DL to NORMAL policy, matching the
existing behavior in __setscheduler_params().
Note: this fix alone requires a correct default_timer_slack_ns to be
effective. See the following patch for that fix.
Fixes: ed4fb6d7ef ("hrtimer: Use and report correct timerslack values for realtime tasks")
Reported-by: Qiaoting.Lin <linqiaoting@xiaomi.com>
Signed-off-by: Guanyou.Chen <chenguanyou@xiaomi.com>
Signed-off-by: Chunhui.Li <chunhui.li@mediatek.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260522131000.1664983-2-chenguanyou@xiaomi.com
Rather than gate the proxy paths with p->blocked_on, use p->is_blocked.
This opens up the state: '->is_blocked && !->blocked_on' for future use.
Notably, only proxy and delayed tasks can be ->on_rq && ->is_blocked, and it is
guaranteed that sched_class::pick_task() will never return a delayed task.
Therefore any task returned from pick_next_task() that has ->is_blocked set,
must be a proxy task.
Suggested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260526113322.477954312%40infradead.org
Current code will 'unconditionally' return migrate on PROXY_WAKING, even if the
task is (still) on the original CPU.
Check task_cpu(p) against p->waking_cpu, which per proxy_set_task_cpu()
preserves the original CPU the task was on. If they do not mis-match, there is
no need to go through the more expensive wakeup path.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260527082916.GP3126523%40noisy.programming.kicks-ass.net
The reason for the clause in try_to_wake_up() is, per its comment, that
find_proxy_task()'s proxy_deactivate() is not always called with a cleared
p->blocked_on.
However, that seems silly and easily cured. Make sure to always call
proxy_deactivate() with a cleared p->blocked_on such that we might remove this
clause from the common wake-up path.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: John Stultz <jstultz@google.com>
Link: https://patch.msgid.link/20260526113322.244729903%40infradead.org
Add a new is_blocked flag to the task struct. This flag is set
by try_to_block_task() and cleared by ttwu_do_wakeup() and
tracks if the task is blocked.
Traditionally this would mirror !p->on_rq, however due things
like DELAY_DEQUEUE and PROXY_EXEC, this can diverge, so its
useful to manage separately.
Additionally with this, we might be able to get rid of the
p->se.sched_delayed (ab)use in the core code (eventually).
Taken whole cloth from Peter's email:
https://lore.kernel.org/lkml/20260501132143.GC1026330@noisy.programming.kicks-ass.net/
With a few additional p->is_blocked = 0 in a few cases where
we return current if blocked_on gets zeroed or there is
no owner. This may hint that these current special cases
might be dropped eventually.
This change also helps resolve wait-queue stalls seen with
proxy-execution. See previous patch attempts for details:
https://lore.kernel.org/lkml/20260430215103.2978955-2-jstultz@google.com/
Reported-by: Vineeth Pillai <vineethrp@google.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260512025635.2840817-7-jstultz@google.com
This patch adds logic so try_to_wake_up() will notice if we are
waking a task where blocked_on == PROXY_WAKING, and if necessary
dequeue the task so the wakeup will naturally return-migrate the
donor task back to a cpu it can run on.
This helps performance as we do the dequeue and wakeup under the
locks normally taken in the try_to_wake_up() and avoids having
to do proxy_force_return() from __schedule(), which has to
re-take similar locks and then force a pick again loop.
This was split out from the larger proxy patch, and
significantly reworked.
Credits for the original patch go to:
Peter Zijlstra (Intel) <peterz@infradead.org>
Juri Lelli <juri.lelli@redhat.com>
Valentin Schneider <valentin.schneider@arm.com>
Connor O'Brien <connoro@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260512025635.2840817-6-jstultz@google.com
The DL scheduler keeps the current task in the rbtree, since
the deadline value isn't usually chagned while the task is
runnable.
This results in set_next_task() and put_prev_task() being
simpler, but unfortunately this causes complexity elsewhere.
Specifically when update_curr_dl() updates the deadline, it has
to dequeue and then enqueue the task.
From put_prev_task_dl(), we first call update_curr_dl(), and
then call enqueue_pushable_dl_task().
However, with Proxy Exec this goes awry. Since when a mutex is
released, we might wake the waiting rq->donor. This will cause
put_prev_task() to be called on the donor to take it off the
cpu for return migration.
At that point, from put_prev_task_dl() the update_curr_dl()
logic will dequeue & enqueue the task, and the enqueue function
will call enqueue_pushable_dl_task() (since the task_current()
check won't prevent it). Then back up the callstack in
put_prev_task_dl() we'll end up calling
enqueue_pushable_dl_task() again, tripping the
!RB_EMPTY_NODE(&p->pushable_dl_tasks) warning.
So to avoid this, use Peter's suggested[1] approach, and add a
dl_rq->curr pointer that is set/cleared from set_next_task()/
put_prev_task(), which effectively tracks the rq->donor. We can
then use this to avoid adding the active donor to the pushable
list from enqueue_task_dl().
[1]: https://lore.kernel.org/lkml/20260304095123.GP606826@noisy.programming.kicks-ass.net/
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260512025635.2840817-4-jstultz@google.com
Historically, the prev value from __schedule() was the rq->curr.
This prev value is passed down through numerous functions, and
used in the class scheduler implementations. The fact that
prev was on_cpu until the end of __schedule(), meant it was
stable across the rq lock drops that the class->balance()
implementations often do.
However, with proxy-exec, the prev passed to functions called
by __schedule() is rq->donor, which may not be the same as
rq->curr and may not be on_cpu, this makes the prev value
potentially unstable across rq lock drops.
A recently found issue with proxy-exec, is when we begin doing
return migration from try_to_wake_up(), its possible we may be
waking up the rq->donor. When we do this, we proxy_resched_idle()
to put_prev_set_next() setting the rq->donor to rq->idle, allowing
the rq->donor to be return migrated and allowed to run.
This however runs into trouble, as on another cpu we might be in
the middle of calling __schedule(). Conceptually the rq lock is
held for the majority of the time, but in calling prev_balance()
its possible the class->balance() handler call may briefly drop the rq lock.
This opens a window for try_to_wake_up() to wake and return migrate the
rq->donor before the class logic reacquires the rq lock.
Unfortunately prev_balance() pass in a prev argument, to which we pass
rq->donor. However this prev value can now become stale and incorrect across a
rq lock drop.
So, to correct this, rework the prev_balance() call so that it does not take a
"prev" argument.
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20260512025635.2840817-2-jstultz@google.com
Vineeth found came up with a test driver that could trip up
workqueue stalls. After fixing one issue this test found,
Vineeth reported the test was still failing.
Greatly simplified, a task that tries to take a mutex already
owned by another task that is sleeping, can hit a edge case in
the mutex_lock_common() case.
If the task fails to get the lock, calls into schedule, but gets
a spurious wakeup, it will find that it is first waiter, and
go into the mutex_optimistic_spin() logic. Though before calling
mutex_optimistic_spin(), we clear task blocked_on state, since
mutex_optimistic_spin() may call schedule() if need_resched() is
set.
After mutex_optimistic_spin() fails, we set blocked_on again,
restart the main mutex loop, try to take the lock and call into
schedule_preempt_disabled().
From there, with proxy-execution, we'll see the task is
blocked_on, follow the chain, see the owner is sleeping and
dequeue the waiting task from the runqueue.
This all sounds fine and reasonable. But what I had missed is
that in mutex_optimistic_spin(), not only do we call schedule()
but we set TASK_RUNNABLE right before doing so.
This is ok for that invocation of schedule(). But when we come
back we re-set the blocked_on we had just cleared, but we do not
re-set the task state to TASK_INTERRUPTIBLE/UNINTERRUPTIBLE.
This means we have a task that is blocked_on & TASK_RUNNABLE,
so when the proxy execution code dequeues the task, we are
in trouble since future wakeups will be shortcut by the
ttwu_state_match() check.
Thus, to avoid this, after mutex_optimistic_spin(), set the task
state back when we set blocked_on.
Many many thanks again to Vineeth for his very useful testing
driver that uncovered this long hidden bug, that I hadn't
tripped in all my testing! Very impressed with the problems he's
uncovered!
Reported-by: Vineeth Pillai <vineethrp@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Vineeth Pillai <vineethrp@google.com>
Link: https://patch.msgid.link/20260430215103.2978955-3-jstultz@google.com
system_time_snapshot::systime provides the same information as
system_time_snapshot::real when the snapshot was taken with
ktime_get_snapshot_id(CLOCK_REALTIME).
Convert the history interpolation over to use 'systime' and 'monoraw' as
'real/raw' are going away once all users are converted.
As a side effect this is the first step to support CLOCK_AUX with
get_device_crosstime_stamp() and the history interpolation.
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: David Woodhouse <dwmw@amazon.co.uk>
Tested-by: Arthur Kiyanovski <akiyano@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260529195557.024415766@kernel.org
ktime_get_snapshot() provides a snapshot of the underlying clocksource
counter value and the corresponding CLOCK_MONOTONIC_RAW, CLOCK_REALTIME and
CLOCK_BOOTTIME timestamps.
There is no usage of CLOCK_REALTIME and CLOCK_BOOTTIME at the same time and
CLOCK_BOOTTIME support was just added for the ARM64 KVM tracing mechanism,
which needs CLOCK_BOOTTIME and the underlying clocksource counter value.
ktime_get_snapshot() is also not suitable for usage with CLOCK_AUX, but
that's a prerequisite to support PTP hardware timestamping for CLOCK_AUX
steering.
As a first step, rename ktime_get_snapshot() to ktime_get_snapshot_id(),
which now takes a clockid argument to select the clock which needs to be
captured. The result is stored in system_time_snapshot::systime, which will
replace the system_time_snapshot::real/boot members once all usage sites
have been converted.
ktime_get_snapshot() is a simple wrapper which hands in CLOCK_REALTIME as
clockid argument for the conversion period. That means CLOCK_REALTIME is
now captured twice, but that redunancy is only temporary.
As all usage sites of struct system_time_snapshot has to be updated anyway,
rename the 'raw' member to 'monoraw' for clarity.
No functional change vs. current users of ktime_get_snapshot()
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Tested-by: David Woodhouse <dwmw@amazon.co.uk>
Tested-by: Arthur Kiyanovski <akiyano@amazon.com>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260529195556.971591633@kernel.org
Frederic Weisbecker
Naveen Kumar Chaudhary
Maoyi Xie
Uladzislau Rezki (Sony)
Arnd Bergmann
Siddharth Nayyar
Steven Rostedt
Peter Zijlstra
K Prateek Nayak
Zecheng Li
Guanyou.Chen
John Stultz
Thomas Gleixner
Carlos Llamas