Re: [PATCH] blk-mq: fix selecting software ctx for request

Ming Lei
2020-02-03T12:30:05Z

On Mon, Feb 03, 2020 at 06:28:15PM +0800, Hillf Danton wrote:
>
> Hi Ming
>
> On Mon, 3 Feb 2020 17:16:02 +0800 Ming Lei wrote:
> > On Sun, Feb 02, 2020 at 06:20:04PM +0800, Hillf Danton wrote:
> > >
> > > Select the current cpu if it's mapped to hardware to make helpers like
> > > blk_mq_rq_cpu() return correct value.
> > >
> > > Signed-off-by: Hillf Danton <hdanton@sina.com>
> > > ---
> > >
> > > --- a/block/blk-mq.c
> > > +++ b/block/blk-mq.c
> > > @@ -454,7 +454,10 @@ struct request *blk_mq_alloc_request_hct
> > > blk_queue_exit(q);
> > > return ERR_PTR(-EXDEV);
> > > }
> > > - cpu = cpumask_first_and(alloc_data.hctx->cpumask, cpu_online_mask);
> > > + cpu = raw_smp_processor_id();
> > > + if (!cpumask_test_cpu(cpu, alloc_data.hctx->cpumask))
> > > + cpu = cpumask_first_and(alloc_data.hctx->cpumask,
> > > + cpu_online_mask);
> >
> > How can you know if there is any online CPU available for this hctx?
>
> I don't except for the current cpu.

The current CPU may not belong to hctx->cpumask for blk_mq_alloc_request_hctx(),
that is why I think this API is very weird.

Thanks,
Ming