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?
> 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.
> Signed-off-by: Bart Van Assche <[email protected]>
> Cc: Ming Lei <[email protected]>
> Cc: Omar Sandoval <[email protected]>
> Cc: Christoph Hellwig <[email protected]>
> Cc: Hannes Reinecke <[email protected]>
> Cc: Johannes Thumshirn <[email protected]>
> ---
> block/blk-mq-sched.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
> index d8e3533d3218..c4e0cb5f6f1f 100644
> --- a/block/blk-mq-sched.c
> +++ b/block/blk-mq-sched.c
> @@ -208,8 +208,8 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx
> *hctx)
> * on the dispatch list or we were able to dispatch from the
> * dispatch list.
> */
> + blk_mq_sched_mark_restart_hctx(hctx);
This looks over-kill.
It means RESTART has to be done from request's completion after each new
dispatch.
> if (!list_empty(&rq_list)) {
> - blk_mq_sched_mark_restart_hctx(hctx);
> if (blk_mq_dispatch_rq_list(q, &rq_list, false)) {
> if (has_sched_dispatch)
> blk_mq_do_dispatch_sched(hctx);
> --
> 2.15.0
>
--
Ming
