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block: rearrange a few request fields for better cache layout

Browse source 
Move completion related items (like the call single data) near the
end of the struct, instead of mixing them in with the initial
queueing related fields.

Move queuelist below the bio structures. Then we have all
queueing related bits in the first cache line.

This yields a 1.5-2% increase in IOPS for a null_blk test, both for
sync and for high thread count access. Sync test goes form 975K to
992K, 32-thread case from 20.8M to 21.2M IOPS.

Reviewed-by: Bart Van Assche <[email protected]>
Reviewed-by: Omar Sandoval <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>
This commit is contained in:
Jens Axboe 2018-01-10 11:46:39 -07:00
commit 7c3fb70f03
2 changed files with 24 additions and 22 deletions
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18
block/blk-mq.c
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@ -270,8 +270,6 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
struct blk_mq_tags *tags = blk_mq_tags_from_data(data);
struct request *rq = tags->static_rqs[tag];
rq->rq_flags = 0;
if (data->flags & BLK_MQ_REQ_INTERNAL) {
rq->tag = -1;
rq->internal_tag = tag;
@ -285,26 +283,22 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
data->hctx->tags->rqs[rq->tag] = rq;
}
INIT_LIST_HEAD(&rq->queuelist);
/* csd/requeue_work/fifo_time is initialized before use */
rq->q = data->q;
rq->mq_ctx = data->ctx;
rq->rq_flags = 0;
rq->cpu = -1;
rq->cmd_flags = op;
if (data->flags & BLK_MQ_REQ_PREEMPT)
rq->rq_flags |= RQF_PREEMPT;
if (blk_queue_io_stat(data->q))
rq->rq_flags |= RQF_IO_STAT;
rq->cpu = -1;
INIT_LIST_HEAD(&rq->queuelist);
INIT_HLIST_NODE(&rq->hash);
RB_CLEAR_NODE(&rq->rb_node);
rq->rq_disk = NULL;
rq->part = NULL;
rq->start_time = jiffies;
#ifdef CONFIG_BLK_CGROUP
rq->rl = NULL;
set_start_time_ns(rq);
rq->io_start_time_ns = 0;
#endif
rq->nr_phys_segments = 0;
#if defined(CONFIG_BLK_DEV_INTEGRITY)
rq->nr_integrity_segments = 0;
@ -321,6 +315,12 @@ static struct request *blk_mq_rq_ctx_init(struct blk_mq_alloc_data *data,
rq->end_io_data = NULL;
rq->next_rq = NULL;
#ifdef CONFIG_BLK_CGROUP
rq->rl = NULL;
set_start_time_ns(rq);
rq->io_start_time_ns = 0;
#endif
data->ctx->rq_dispatched[op_is_sync(op)]++;
return rq;
}