From: Chunguang Xu <broo...@tencent.com>
From: Chunguang Xu <broo...@tencent.com>
The IO depth of idle_class 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 <broo...@tencent.com>
---
block/bfq-iosched.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index ec482e6641ff..ea9d7f6f4e3d 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -4808,6 +4808,17 @@ static struct request *__bfq_dispatch_request(struct
blk_mq_hw_ctx *hctx)
if (!bfqq)
goto exit;
+ /*
+ * Here, the IO depth of idle_class 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) {
--
2.30.0
