diff mbox series

[v3,05/14] bfq: limit the IO depth of CLASS_IDLE to 1

Message ID 43daae87ff5fd6ed66e7859b8bc17818f309b9ff.1616649216.git.brookxu@tencent.com (mailing list archive)
State New, archived
Headers show
Series bfq: introduce bfq.ioprio for cgroup | expand

Commit Message

brookxu March 25, 2021, 6:57 a.m. UTC
From: Chunguang Xu <brookxu@tencent.com>

The IO depth of queues belong to CLASS_IDLE is limited to 1,
so that it can avoid introducing a larger tail latency under
a device with a larger IO depth. Although limiting the IO
depth may reduce the performance of idle_class, it is
generally not a big problem, because idle_class usually does
not have strict performance requirements.

Signed-off-by: Chunguang Xu <brookxu@tencent.com>
---
 block/bfq-iosched.c | 11 +++++++++++
 1 file changed, 11 insertions(+)
diff mbox series

Patch

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 5f7a0cc..8eaf0eb 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4831,6 +4831,17 @@  static struct request *__bfq_dispatch_request(struct blk_mq_hw_ctx *hctx)
 	if (!bfqq)
 		goto exit;
 
+	/*
+	 * Here, the IO depth of queues belong to CLASS_IDLE is limited
+	 * to 1, so that it can avoid introducing a larger tail latency
+	 * under a device with a larger IO depth. Although limiting the
+	 * IO depth may reduce the performance of idle_class, it is
+	 * generally not a big problem, because idle_class usually
+	 * does not have strict performance requirements.
+	 */
+	if (bfq_class_idle(bfqq) && bfqq->dispatched)
+		goto exit;
+
 	rq = bfq_dispatch_rq_from_bfqq(bfqd, bfqq);
 
 	if (rq) {