Hi,

On Thursday, September 11, 2014 02:42:49 PM Alexander Gordeev wrote:

The numbers are taken by running 'dd if=/dev/sd{a,b} of=/dev/null'
in parallel. All time values are in us.

Before this update host lock average holdtime was 2.45 and
average waittime was 1.24. After the update average holdtime
dropped to 0.29 (about eight times) while average waittime
decreased to 0.58 (about two times).

Also, port events are handled with local interrupts enabled
and compete on individual per-port locks with average holdtime
1.25 and average waittime 1.48. So combined average holdtime
spent while holding host and port locks decreased from 2.45 to
0.29 + 1.25 = 1.54 (about 1.6 times).

The downside of this change is introduction of a kernel thread.

The upside is shorter access time to port locks and moving port
interrupts handling out of the hardware interrupt context.

IMHO it would be great to put the above results into the patch
description (it now looks a bit skimpy).

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics