For block devices that call blk_mq_complete_request() to end request
in process context, it's pointless to redirect the completion to be
done in block soft-irq, also blk_mq_raise_softirq() isnt't a very
light operation, which contains preempt and hard irq disable, wake
up ksoftirqd in non-interrupt context.
I found this issue while I use tcm_loop and tcmu(backstore is file)
to evaluate performance, tcm_loop end request in workqueue.
Without this patch: libaio engine, direct io, randwrite, io size 128k
job0: (groupid=0, jobs=1): err= 0: pid=20876: Thu Jan 27 15:33:45 2022
write: IOPS=15.7k, BW=1966MiB/s (2062MB/s)(115GiB/60001msec); 0 zone resets
slat (nsec): min=5675, max=83552, avg=8689.69, stdev=996.96
clat (usec): min=231, max=99977, avg=498.89, stdev=501.69
lat (usec): min=291, max=99986, avg=507.70, stdev=501.69
With this patch:
job0: (groupid=0, jobs=1): err= 0: pid=12813: Thu Jan 27 15:50:46 2022
write: IOPS=16.8k, BW=2101MiB/s (2203MB/s)(123GiB/60001msec); 0 zone resets
slat (usec): min=5, max=125, avg=14.12, stdev=10.31
clat (usec): min=306, max=65380, avg=460.78, stdev=506.24
lat (usec): min=341, max=65389, avg=475.04, stdev=505.27
Which improves throughput and reduces lat.
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
---
block/blk-mq.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 8874a63ae952..9fdffc65d7ba 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -974,6 +974,9 @@ bool blk_mq_complete_request_remote(struct request *rq)
return true;
}
+ if (!in_interrupt())
+ return false;
+
if (rq->q->nr_hw_queues == 1) {
blk_mq_raise_softirq(rq);
return true;
--
2.14.4.44.g2045bb6
