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block: strict rq_affinity

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Some systems benefit from completions always being steered to the strict
requester cpu rather than the looser "per-socket" steering that
blk_cpu_to_group() attempts by default. This is because the first
CPU in the group mask ends up being completely overloaded with work,
while the others (including the original submitter) has power left
to spare.

Allow the strict mode to be set by writing '2' to the sysfs control
file. This is identical to the scheme used for the nomerges file,
where '2' is a more aggressive setting than just being turned on.

echo 2 > /sys/block/<bdev>/queue/rq_affinity

Cc: Christoph Hellwig <hch@infradead.org>
Cc: Roland Dreier <roland@purestorage.com>
Tested-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Dan Williams 2011-07-23 20:44:25 +02:00 committed by Jens Axboe
parent ef3230880a
commit 5757a6d76c
5 changed files with 27 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
Documentation/block/queue-sysfs.txt
View File

@ -45,9 +45,13 @@ device.
rq_affinity (RW)
----------------
If this option is enabled, the block layer will migrate request completions
to the CPU that originally submitted the request. For some workloads
this provides a significant reduction in CPU cycles due to caching effects.
If this option is '1', the block layer will migrate request completions to the
cpu "group" that originally submitted the request. For some workloads this
provides a significant reduction in CPU cycles due to caching effects.
For storage configurations that need to maximize distribution of completion
processing setting this option to '2' forces the completion to run on the
requesting cpu (bypassing the "group" aggregation logic).
scheduler (RW)
--------------

6
block/blk-core.c
View File

@ -1279,10 +1279,8 @@ get_rq:
init_request_from_bio(req, bio);
if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) ||
bio_flagged(bio, BIO_CPU_AFFINE)) {
req->cpu = blk_cpu_to_group(get_cpu());
put_cpu();
}
bio_flagged(bio, BIO_CPU_AFFINE))
req->cpu = smp_processor_id();
plug = current->plug;
if (plug) {

11
block/blk-softirq.c
View File

@ -103,22 +103,25 @@ static struct notifier_block __cpuinitdata blk_cpu_notifier = {
void __blk_complete_request(struct request *req)
{
int ccpu, cpu, group_cpu = NR_CPUS;
struct request_queue *q = req->q;
unsigned long flags;
int ccpu, cpu, group_cpu;
BUG_ON(!q->softirq_done_fn);
local_irq_save(flags);
cpu = smp_processor_id();
group_cpu = blk_cpu_to_group(cpu);
/*
* Select completion CPU
*/
if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1)
if (test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags) && req->cpu != -1) {
ccpu = req->cpu;
else
if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags)) {
ccpu = blk_cpu_to_group(ccpu);
group_cpu = blk_cpu_to_group(cpu);
}
} else
ccpu = cpu;
if (ccpu == cpu || ccpu == group_cpu) {

13
block/blk-sysfs.c
View File

@ -244,8 +244,9 @@ static ssize_t queue_nomerges_store(struct request_queue *q, const char *page,
static ssize_t queue_rq_affinity_show(struct request_queue *q, char *page)
{
bool set = test_bit(QUEUE_FLAG_SAME_COMP, &q->queue_flags);
bool force = test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags);
return queue_var_show(set, page);
return queue_var_show(set << force, page);
}
static ssize_t
@ -257,10 +258,14 @@ queue_rq_affinity_store(struct request_queue *q, const char *page, size_t count)
ret = queue_var_store(&val, page, count);
spin_lock_irq(q->queue_lock);
if (val)
if (val) {
queue_flag_set(QUEUE_FLAG_SAME_COMP, q);
else
queue_flag_clear(QUEUE_FLAG_SAME_COMP, q);
if (val == 2)
queue_flag_set(QUEUE_FLAG_SAME_FORCE, q);
} else {
queue_flag_clear(QUEUE_FLAG_SAME_COMP, q);
queue_flag_clear(QUEUE_FLAG_SAME_FORCE, q);
}
spin_unlock_irq(q->queue_lock);
#endif
return ret;

3
include/linux/blkdev.h
View File

@ -392,7 +392,7 @@ struct request_queue {
#define QUEUE_FLAG_ELVSWITCH 6 /* don't use elevator, just do FIFO */
#define QUEUE_FLAG_BIDI 7 /* queue supports bidi requests */
#define QUEUE_FLAG_NOMERGES 8 /* disable merge attempts */
#define QUEUE_FLAG_SAME_COMP 9 /* force complete on same CPU */
#define QUEUE_FLAG_SAME_COMP 9 /* complete on same CPU-group */
#define QUEUE_FLAG_FAIL_IO 10 /* fake timeout */
#define QUEUE_FLAG_STACKABLE 11 /* supports request stacking */
#define QUEUE_FLAG_NONROT 12 /* non-rotational device (SSD) */
@ -402,6 +402,7 @@ struct request_queue {
#define QUEUE_FLAG_NOXMERGES 15 /* No extended merges */
#define QUEUE_FLAG_ADD_RANDOM 16 /* Contributes to random pool */
#define QUEUE_FLAG_SECDISCARD 17 /* supports SECDISCARD */
#define QUEUE_FLAG_SAME_FORCE 18 /* force complete on same CPU */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \