Re: 10x I/O await times in 6.12

[Matt Fleming <mfleming@cloudflare.com>]

On Thu, Apr 23, 2026 at 07:18:39PM +0100, Matt Fleming wrote:
> On Mon, Apr 21, 2025 at 08:21:13PM +0800, Yu Kuai wrote:
> > If nsecs - plug->cur_ktime is still milliseconds, can you check if
> > the following patch can fix your problem?
> > 
> > Thanks,
> > Kuai
> > 
> > diff --git a/block/blk-mq.c b/block/blk-mq.c
> > index ae8494d88897..37197502147e 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -1095,7 +1095,9 @@ static inline void blk_account_io_start(struct request
> > *req)
> >                 return;
> > 
> >         req->rq_flags |= RQF_IO_STAT;
> > -       req->start_time_ns = blk_time_get_ns();
> > +
> > +       if (!current->plug)
> > +               req->start_time_ns = blk_time_get_ns();
> > 
> >         /*
> >          * All non-passthrough requests are created from a bio with one
> > @@ -2874,6 +2876,7 @@ void blk_mq_flush_plug_list(struct blk_plug *plug,
> > bool from_schedule)
> >  {
> >         struct request *rq;
> >         unsigned int depth;
> > +       u64 now;
> > 
> >         /*
> >          * We may have been called recursively midway through handling
> > @@ -2887,6 +2890,10 @@ void blk_mq_flush_plug_list(struct blk_plug *plug,
> > bool from_schedule)
> >         depth = plug->rq_count;
> >         plug->rq_count = 0;
> > 
> > +       now = ktime_get_ns();
> > +       rq_list_for_each(&plug->mq_list, rq)
> > +               rq->start_time_ns = now;
> > +
> >         if (!plug->multiple_queues && !plug->has_elevator && !from_schedule)
> > {
> >                 struct request_queue *q;
> > 
> 
> It's April again, and this time we're moving to 6.18.
> 
> The I/O accounting bug reported at the start of this thread is still an
> issue for us, and we've been carrying the above patch for 12 months.

Hey Jens, any feedback on this patch?