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blk-mq: avoid to write intermediate result to hctx->next_cpu 

This patch figures out the final selected CPU, then writes
it to hctx->next_cpu once, then we can avoid to intermediate
next cpu observed from other dispatch paths.

Cc: Stefan Haberland <sth@linux.vnet.ibm.com>
Tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
hifive-unleashed-5.1
Ming Lei 2018-04-08 17:48:09 +08:00 committed by Jens Axboe
parent bffa9909a6
commit 476f8c98a9
1 changed files with 9 additions and 8 deletions
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17
block/blk-mq.c
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@ -1344,26 +1344,24 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
{
bool tried = false;
int next_cpu = hctx->next_cpu;
if (hctx->queue->nr_hw_queues == 1)
return WORK_CPU_UNBOUND;
if (--hctx->next_cpu_batch <= 0) {
int next_cpu;
select_cpu:
next_cpu = cpumask_next_and(hctx->next_cpu, hctx->cpumask,
next_cpu = cpumask_next_and(next_cpu, hctx->cpumask,
cpu_online_mask);
if (next_cpu >= nr_cpu_ids)
next_cpu = cpumask_first_and(hctx->cpumask,cpu_online_mask);
next_cpu = cpumask_first_and(hctx->cpumask, cpu_online_mask);
/*
* No online CPU is found, so have to make sure hctx->next_cpu
* is set correctly for not breaking workqueue.
*/
if (next_cpu >= nr_cpu_ids)
hctx->next_cpu = cpumask_first(hctx->cpumask);
else
hctx->next_cpu = next_cpu;
next_cpu = cpumask_first(hctx->cpumask);
hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
}
@ -1371,7 +1369,7 @@ select_cpu:
* Do unbound schedule if we can't find a online CPU for this hctx,
* and it should only happen in the path of handling CPU DEAD.
*/
if (!cpu_online(hctx->next_cpu)) {
if (!cpu_online(next_cpu)) {
if (!tried) {
tried = true;
goto select_cpu;
@ -1381,10 +1379,13 @@ select_cpu:
* Make sure to re-select CPU next time once after CPUs
* in hctx->cpumask become online again.
*/
hctx->next_cpu = next_cpu;
hctx->next_cpu_batch = 1;
return WORK_CPU_UNBOUND;
}
return hctx->next_cpu;
hctx->next_cpu = next_cpu;
return next_cpu;
}
static void __blk_mq_delay_run_hw_queue(struct blk_mq_hw_ctx *hctx, bool async,