Re: [PATCH 2/2] blk-mq: simplify queue mapping & schedule with each possisble CPU

[Ming Lei]

On Wed, Jan 17, 2018 at 11:07:48AM +0100, Christian Borntraeger wrote:
> 
> 
> On 01/17/2018 10:57 AM, Ming Lei wrote:
> > Hi Jianchao,
> > 
> > On Wed, Jan 17, 2018 at 04:09:11PM +0800, jianchao.wang wrote:
> >> Hi ming 
> >>
> >> Thanks for your kindly response.
> >>
> >> On 01/17/2018 02:22 PM, Ming Lei wrote:
> >>> This warning can't be removed completely, for example, the CPU figured
> >>> in blk_mq_hctx_next_cpu(hctx) can be put on again just after the
> >>> following call returns and before __blk_mq_run_hw_queue() is scheduled
> >>> to run.
> >>>
> >>> 	kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work, msecs_to_jiffies(msecs))
> >> We could use cpu_active in __blk_mq_run_hw_queue() to narrow the window.
> >> There is a big gap between cpu_online and cpu_active. rebind_workers is also between them.
> > 
> > This warning is harmless, also you can't reproduce it without help of your
> > special patch, I guess, :-) So the window shouldn't be a big deal. 
> 
> FWIW, every WARN_ON is problematic since there are people running with panic_on_warn.
> If a condition can happen we should not use WARN_ON but something else.

Agree, printk() should be fine, IMO.


-- 
Ming