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block: add support for IO CPU affinity

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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>
This commit is contained in:
Jens Axboe 2008-09-13 20:26:01 +02:00
parent 18887ad910
commit c7c22e4d5c
9 changed files with 182 additions and 60 deletions
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5
include/linux/blkdev.h
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@ -17,6 +17,7 @@
#include <linux/module.h>
#include <linux/stringify.h>
#include <linux/bsg.h>
#include <linux/smp.h>
#include <asm/scatterlist.h>
@ -139,7 +140,8 @@ enum rq_flag_bits {
*/
struct request {
struct list_head queuelist;
struct list_head donelist;
struct call_single_data csd;
int cpu;
struct request_queue *q;
@ -420,6 +422,7 @@ struct request_queue
#define QUEUE_FLAG_ELVSWITCH 8 /* don't use elevator, just do FIFO */
#define QUEUE_FLAG_BIDI 9 /* queue supports bidi requests */
#define QUEUE_FLAG_NOMERGES 10 /* disable merge attempts */
#define QUEUE_FLAG_SAME_COMP 11 /* force complete on same CPU */
static inline int queue_is_locked(struct request_queue *q)
{