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[PATCH 2/2] tty: Use unbound workqueue for all input workers

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  [PATCH 2/2] tty: Use unbound workqueue for all input workers Peter Hurley <peter@hurleysoftware.com> - 2015-10-17 22:40 +0200
    Re: [PATCH 2/2] tty: Use unbound workqueue for all input workers Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2015-10-18 06:40 +0200

#1249450 — [PATCH 2/2] tty: Use unbound workqueue for all input workers

The commonly accepted wisdom that scheduling work on the same cpu
that handled interrupt i/o benefits from cache-locality is only
true if the cpu is idle (since bound kworkers are often the highest
vruntime and thus the lowest priority).

Measurements of scheduling via the unbound queue show lowered
worst-case latency responses of up to 5x over bound workqueue, without
increase in average latency or throughput.

pty i/o test measurements show >3x (!) reduced total running time; tests
previously taking ~8s now complete in <2.5s.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
---
 drivers/tty/tty_buffer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 7cc16db..9a479e6 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -403,7 +403,7 @@ void tty_schedule_flip(struct tty_port *port)
 	 * flush_to_ldisc() sees buffer data.
 	 */
 	smp_store_release(&buf->tail->commit, buf->tail->used);
-	schedule_work(&buf->work);
+	queue_work(system_unbound_wq, &buf->work);
 }
 EXPORT_SYMBOL(tty_schedule_flip);
 
-- 
2.6.1

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#1249988

On Sat, Oct 17, 2015 at 04:36:24PM -0400, Peter Hurley wrote:
> The commonly accepted wisdom that scheduling work on the same cpu
> that handled interrupt i/o benefits from cache-locality is only
> true if the cpu is idle (since bound kworkers are often the highest
> vruntime and thus the lowest priority).
> 
> Measurements of scheduling via the unbound queue show lowered
> worst-case latency responses of up to 5x over bound workqueue, without
> increase in average latency or throughput.
> 
> pty i/o test measurements show >3x (!) reduced total running time; tests
> previously taking ~8s now complete in <2.5s.

Wow, nice job with this, that's unexpected.

greg k-h
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