Re: [PATCH RFC] scsi: core: remove unsed 'restarts' from scsi_device

[Yu Kuai]

在 2022/11/28 11:27, Ming Lei 写道:
> On Sat, Nov 26, 2022 at 04:54:46PM +0800, Yu Kuai wrote:
> > Hi,
> >
> > 在 2022/11/18 19:30, Yu Kuai 写道:
> > > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> > >
> > > During code review, I found that 'restarts' is not useful anymore after
> > > the following commits:
> > >
> > > 1) commit ab3cee3762e5 ("blk-mq: In blk_mq_dispatch_rq_list() "no budget"
> > > is a reason to kick")
> > > 2) commit d3b38596875d ("blk-mq: run queue no matter whether the request
> > > is the last request")
> > > 3) commit 673235f91531 ("scsi: core: Fix race between handling STS_RESOURCE
> > > and completion")
> > >
> > > Now that if get budget ever failed, block layer will make sure to
> > > trigger new run queue for the hctx. Hence there is no need to run queue
> > > from scsi layer in this case.
>
> But scsi_run_queue_async() needs to run all hw queue because budget is
> actually LUN/request queue wide.

Why the hw queue need to run if get budget never failed in this hw
queue?

> > Does anyone has suggestions about this patch?
> >
> > More info why I tried to remove this:
> >
> > while testing megaraid with 4 nvme with none elevator, the default
> > queue_depth is 128, while I test it with fio 128 jobs and 1 iodepth,
> > bw is about 4Gib/s, however, if I test with 128 jobs and 2 iodepth,
> > bw is decreased to about 0.8Gib/s, and with this patch applied,
> > bw can stay 4Gib/s in the later case.
>
> What is .can_queue and nr_hw_queues in your setting?
test cmd:
fio -name=0 -ioengine=libaio -direct=1 -group_reporting=1 -randseed=2022 
-rwmixread=70 -refill_buffers -filename=/dev/sdg -numjobs=128 -size=1TB 
-runtime=60s -bs=4k -iodepth=2 -rw=randwrite

test environment:
arm64 Kunpeng-920, 128 cpu
megaraid with 4 NVMEs, 128 hctx and queue_depth is 128

> thanks,
> Ming
>
> .