On Fri, 2017-12-01 at 10:58 +0800, Ming Lei wrote:
> On Thu, Nov 30, 2017 at 04:08:45PM -0800, Bart Van Assche wrote:
> > blk_mq_sched_mark_restart_hctx() must be called before
>
> Could you please describe the theory on commit log? Like, why is it
> a must? and what is the issue to be fixed?
The BLK_MQ_S_SCHED_RESTART test at the end of blk_mq_dispatch_rq_list() can
only work if BLK_MQ_S_SCHED_RESTART is set before blk_mq_dispatch_rq_list()
is called. BTW, without this patch every iteration of my test triggers a
queue stall. With this patch a queue stall only occurs sporadically so I
think we really need something like this patch.
> > blk_mq_dispatch_rq_list() is called. Make sure that
> > BLK_MQ_S_SCHED_RESTART is set before any blk_mq_dispatch_rq_list()
> > call occurs.
> >
> > Fixes: commit b347689ffbca ("blk-mq-sched: improve dispatching from sw queue")
>
> We always mark RESTART state bit just before dispatching from ->dispatch_list,
> this way has been there before b347689ffbca, which doesn't change this
> RESTART mechanism, so please explain a bit why it is a fix on commit
> b347689ffbca.
I'm not completely sure which patch introduced the lockup fixed by this patch
but I will have another look whether this was really introduced by commit
b347689ffbca.
Bart.
