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Commit 8e3fba55 authored by Bryan O'Donoghue's avatar Bryan O'Donoghue Committed by Greg Kroah-Hartman
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greybus: loopback: Add asynchronous backoff 



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: default avatarJohan Hovold <johan@hovoldconsulting.com>
Signed-off-by: default avatarBryan O'Donoghue <bryan.odonoghue@linaro.org>
Reviewed-by: default avatarJohan Hovold <johan@hovoldconsulting.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@google.com>
parent 36f241ff

drivers/staging/greybus/loopback.c

+18 −0
Original line number Diff line number Diff line
@@ -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;