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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 7cc16db37e0e7ae6be67b6f81515de10ea83a0da..9a479e61791a2a80cd0ae3fd5c93c6d0873d6998 100644 (file)
--- 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);