linux-kernel - Re: [PATCH] sched: use rq_lock/unlock in online_fair_sched

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Message-ID: <20190805140653.GA20173@pauld.bos.csb>
Date:   Mon, 5 Aug 2019 10:06:53 -0400
From:   Phil Auld <pauld@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH] sched: use rq_lock/unlock in online_fair_sched_group

On Fri, Aug 02, 2019 at 05:20:38PM +0800 Hillf Danton wrote:
> 
> On Thu,  1 Aug 2019 09:37:49 -0400 Phil Auld wrote:
> >
> > Enabling WARN_DOUBLE_CLOCK in /sys/kernel/debug/sched_features causes
> > warning to fire in update_rq_clock. This seems to be caused by onlining
> > a new fair sched group not using the rq lock wrappers.
> > 
> > [472978.683085] rq->clock_update_flags & RQCF_UPDATED
> > [472978.683100] WARNING: CPU: 5 PID: 54385 at kernel/sched/core.c:210 update_rq_clock+0xec/0x150
> 
> Another option perhaps only if that wrappers are not mandatory.
> 
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -212,10 +212,14 @@ void update_rq_clock(struct rq *rq)
>  #endif
>  
>  	delta = sched_clock_cpu(cpu_of(rq)) - rq->clock;
> -	if (delta < 0)
> -		return;
> -	rq->clock += delta;
> -	update_rq_clock_task(rq, delta);
> +	if (delta >= 0) {
> +		rq->clock += delta;
> +		update_rq_clock_task(rq, delta);
> +	}
> +
> +#ifdef CONFIG_SCHED_DEBUG
> +	rq->clock_update_flags &= ~RQCF_UPDATED;
> +#endif
>  }
>  
>  
> --
> 

I think that would silence the warning, but...

If we're to clear that flag right there, outside of the lock pinning code, 
then I think we might as well just remove the flag and all associated 
comments etc, no?


Cheers,
Phil

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