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greybus: loopback: Add asynchronous backoff

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A specific request from the firmware people is the ability to back-off from
sending more asynchronous operations once a specific number of operations
are in-flight.

This patch adds that ability - with a new sysfs parameter
'outstanding_operations_max' which controls the maximum number of
operations that can be outstanding/in-flight at any time.

When outstanding_operations_max contains a non-zero value and asynchronous
operations are being used - we will back-off until the completion counter
is < outstanding_operations_max. Tested in both synchronous and
asynchronous mode and with gb_loopback_connection_exit() interrupting
in-flight operations.

Suggested-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
This commit is contained in:
Bryan O'Donoghue
2015-12-11 13:46:53 +00:00
committed by Greg Kroah-Hartman
parent 36f241fff4
commit 8e3fba55d3
1 changed files with 18 additions and 0 deletions
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drivers/staging/greybus/loopback.c
+18
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@@ -98,6 +98,7 @@ struct gb_loopback {
u32 jiffy_timeout;
u32 timeout_min;
u32 timeout_max;
u32 outstanding_operations_max;
u32 lbid;
u64 elapsed_nsecs;
u32 apbridge_latency_ts;
@@ -311,6 +312,8 @@ gb_dev_loopback_ro_attr(iteration_count, false);
gb_dev_loopback_rw_attr(async, u);
/* Timeout of an individual asynchronous request */
gb_dev_loopback_rw_attr(timeout, u);
/* Maximum number of in-flight operations before back-off */
gb_dev_loopback_rw_attr(outstanding_operations_max, u);
static struct attribute *loopback_attrs[] = {
&dev_attr_latency_min.attr,
@@ -338,6 +341,7 @@ static struct attribute *loopback_attrs[] = {
&dev_attr_requests_completed.attr,
&dev_attr_requests_timedout.attr,
&dev_attr_timeout.attr,
&dev_attr_outstanding_operations_max.attr,
&dev_attr_timeout_min.attr,
&dev_attr_timeout_max.attr,
NULL,
@@ -911,6 +915,16 @@ static void gb_loopback_calculate_stats(struct gb_loopback *gb)
gb->gpbridge_latency_ts);
}
static void gb_loopback_async_wait_to_send(struct gb_loopback *gb)
{
if (!(gb->async && gb->outstanding_operations_max))
return;
wait_event_interruptible(gb->wq_completion,
(atomic_read(&gb->outstanding_operations) <
gb->outstanding_operations_max) ||
kthread_should_stop());
}
static int gb_loopback_fn(void *data)
{
int error = 0;
@@ -924,7 +938,11 @@ static int gb_loopback_fn(void *data)
if (!gb->type)
wait_event_interruptible(gb->wq, gb->type ||
kthread_should_stop());
if (kthread_should_stop())
break;
/* Limit the maximum number of in-flight async operations */
gb_loopback_async_wait_to_send(gb);
if (kthread_should_stop())
break;