From ab3cee3762e5e69f27c302c43691289fdfc12316 Mon Sep 17 00:00:00 2001
From: Douglas Anderson <dianders@chromium.org>
Date: Mon, 20 Apr 2020 09:24:51 -0700
Subject: [PATCH] blk-mq: In blk_mq_dispatch_rq_list() "no budget" is a reason
to kick
Git-commit: ab3cee3762e5e69f27c302c43691289fdfc12316
Patch-Mainline: v5.11-rc1
References: bsc#1214586
In blk_mq_dispatch_rq_list(), if blk_mq_sched_needs_restart() returns
true and the driver returns BLK_STS_RESOURCE then we'll kick the
queue. However, there's another case where we might need to kick it.
If we were unable to get budget we can be in much the same state as
when the driver returns BLK_STS_RESOURCE, so we should treat it the
same.
It should be noted that even if we add a whole bunch of extra kicking
to the queue in other patches this patch is still important.
Specifically any kicking that happened before we re-spliced leftover
requests into 'hctx->dispatch' wouldn't have found any work, so we
really need to make sure we kick ourselves after we've done the
splicing.
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Vasilis Liaskovitis <vliaskovitis@suse.com>
---
block/blk-mq.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1160,6 +1160,7 @@ bool blk_mq_dispatch_rq_list(struct requ
bool no_tag = false;
int errors, queued;
blk_status_t ret = BLK_STS_OK;
+ bool no_budget_avail = false;
if (list_empty(list))
return false;
@@ -1176,8 +1177,10 @@ bool blk_mq_dispatch_rq_list(struct requ
rq = list_first_entry(list, struct request, queuelist);
hctx = blk_mq_map_queue(rq->q, rq->mq_ctx->cpu);
- if (!got_budget && !blk_mq_get_dispatch_budget(hctx))
+ if (!got_budget && !blk_mq_get_dispatch_budget(hctx)) {
+ no_budget_avail = true;
break;
+ }
if (!blk_mq_get_driver_tag(rq)) {
/*
@@ -1274,13 +1277,15 @@ bool blk_mq_dispatch_rq_list(struct requ
*
* If driver returns BLK_STS_RESOURCE and SCHED_RESTART
* bit is set, run queue after a delay to avoid IO stalls
- * that could otherwise occur if the queue is idle.
+ * that could otherwise occur if the queue is idle. We'll do
+ * similar if we couldn't get budget and SCHED_RESTART is set.
*/
needs_restart = blk_mq_sched_needs_restart(hctx);
if (!needs_restart ||
(no_tag && list_empty_careful(&hctx->dispatch_wait.entry)))
blk_mq_run_hw_queue(hctx, true);
- else if (needs_restart && (ret == BLK_STS_RESOURCE))
+ else if (needs_restart && (ret == BLK_STS_RESOURCE ||
+ no_budget_avail))
blk_mq_delay_run_hw_queue(hctx, BLK_MQ_RESOURCE_DELAY);
blk_mq_update_dispatch_busy(hctx, true);