tree ecc3d2517b3471ccc35d4cb4e3b48d4b57205061
parent 18887ad910e56066233a07fd3cfb2fa11338b782
author Jens Axboe <jens.axboe@oracle.com> 1221330361 +0200
committer Jens Axboe <jens.axboe@oracle.com> 1223535369 +0200

block: add support for IO CPU affinity

This patch adds support for controlling the IO completion CPU of
either all requests on a queue, or on a per-request basis. We export
a sysfs variable (rq_affinity) which, if set, migrates completions
of requests to the CPU that originally submitted it. A bio helper
(bio_set_completion_cpu()) is also added, so that queuers can ask
for completion on that specific CPU.

In testing, this has been show to cut the system time by as much
as 20-40% on synthetic workloads where CPU affinity is desired.

This requires a little help from the architecture, so it'll only
work as designed for archs that are using the new generic smp
helper infrastructure.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>