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net: poll/select low latency socket support

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select/poll busy-poll support.

Split sysctl value into two separate ones, one for read and one for poll.
updated Documentation/sysctl/net.txt

Add a new poll flag POLL_LL. When this flag is set, sock_poll will call
sk_poll_ll if possible. sock_poll sets this flag in its return value
to indicate to select/poll when a socket that can busy poll is found.

When poll/select have nothing to report, call the low-level
sock_poll again until we are out of time or we find something.

Once the system call finds something, it stops setting POLL_LL, so it can
return the result to the user ASAP.

Signed-off-by: Eliezer Tamir <eliezer.tamir@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eliezer Tamir
2013-06-24 10:28:03 +03:00
committed by David S. Miller
parent e4f2379db6
commit 2d48d67fa8
7 changed files with 91 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/net/ll_poll.h
+22 -13
View File
@@ -30,6 +30,7 @@
#ifdef CONFIG_NET_LL_RX_POLL
struct napi_struct;
extern unsigned int sysctl_net_ll_read __read_mostly;
extern unsigned int sysctl_net_ll_poll __read_mostly;
/* return values from ndo_ll_poll */
@@ -38,17 +39,18 @@ extern unsigned int sysctl_net_ll_poll __read_mostly;
/* we can use sched_clock() because we don't care much about precision
* we only care that the average is bounded
* we don't mind a ~2.5% imprecision so <<10 instead of *1000
* sk->sk_ll_usec is a u_int so this can't overflow
*/
static inline u64 ll_end_time(struct sock *sk)
static inline u64 ll_sk_end_time(struct sock *sk)
{
u64 end_time = ACCESS_ONCE(sk->sk_ll_usec);
return ((u64)ACCESS_ONCE(sk->sk_ll_usec) << 10) + sched_clock();
}
/* we don't mind a ~2.5% imprecision
* sk->sk_ll_usec is a u_int so this can't overflow
*/
end_time = (end_time << 10) + sched_clock();
return end_time;
/* in poll/select we use the global sysctl_net_ll_poll value */
static inline u64 ll_end_time(void)
{
return ((u64)ACCESS_ONCE(sysctl_net_ll_poll) << 10) + sched_clock();
}
static inline bool sk_valid_ll(struct sock *sk)
@@ -62,10 +64,13 @@ static inline bool can_poll_ll(u64 end_time)
return !time_after64(sched_clock(), end_time);
}
/* when used in sock_poll() nonblock is known at compile time to be true
* so the loop and end_time will be optimized out
*/
static inline bool sk_poll_ll(struct sock *sk, int nonblock)
{
u64 end_time = nonblock ? 0 : ll_sk_end_time(sk);
const struct net_device_ops *ops;
u64 end_time = ll_end_time(sk);
struct napi_struct *napi;
int rc = false;
@@ -84,7 +89,6 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock)
goto out;
do {
rc = ops->ndo_ll_poll(napi);
if (rc == LL_FLUSH_FAILED)
@@ -95,8 +99,8 @@ static inline bool sk_poll_ll(struct sock *sk, int nonblock)
NET_ADD_STATS_BH(sock_net(sk),
LINUX_MIB_LOWLATENCYRXPACKETS, rc);
} while (skb_queue_empty(&sk->sk_receive_queue)
&& can_poll_ll(end_time) && !nonblock);
} while (!nonblock && skb_queue_empty(&sk->sk_receive_queue) &&
can_poll_ll(end_time));
rc = !skb_queue_empty(&sk->sk_receive_queue);
out:
@@ -118,7 +122,12 @@ static inline void sk_mark_ll(struct sock *sk, struct sk_buff *skb)
#else /* CONFIG_NET_LL_RX_POLL */
static inline u64 ll_end_time(struct sock *sk)
static inline u64 sk_ll_end_time(struct sock *sk)
{
return 0;
}
static inline u64 ll_end_time(void)
{
return 0;
}