linux-kernel - Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and IO

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Date:   Mon, 6 Aug 2018 18:03:29 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tejun Heo <tj@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Daniel Drake <drake@...lessm.com>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Christopher Lameter <cl@...ux.com>,
        Mike Galbraith <efault@....de>,
        Shakeel Butt <shakeelb@...gle.com>,
        Peter Enderborg <peter.enderborg@...y.com>, linux-mm@...ck.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 8/9] psi: pressure stall information for CPU, memory, and
 IO

On Mon, Aug 06, 2018 at 11:19:28AM -0400, Johannes Weiner wrote:
> On Fri, Aug 03, 2018 at 06:56:41PM +0200, Peter Zijlstra wrote:
> > On Wed, Aug 01, 2018 at 11:19:57AM -0400, Johannes Weiner wrote:

> > > +		u32 uninitialized_var(nonidle);
> > 
> > urgh.. I can see why the compiler got confused. Dodgy :-)
> 
> :-) I think we can make this cleaner. Something like this (modulo the
> READ_ONCE/WRITE_ONCE you pointed out in the other email)?
> 

> @@ -244,60 +287,17 @@ static bool psi_update_stats(struct psi_group *group)
>  	 */
>  	for_each_online_cpu(cpu) {
>  		struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
> +		u32 nonidle;
> +
> +		nonidle = read_update_delta(groupc, PSI_NONIDLE, cpu);
> +		nonidle = nsecs_to_jiffies(nonidle);
> +		nonidle_total += nonidle;
> +
> +		for (s = 0; s < PSI_NONIDLE; s++) {
> +			u32 delta;
> +
> +			delta = read_update_delta(groupc, s, cpu);
> +			deltas[s] += (u64)delta * nonidle;
>  		}
>  	}

Yes, much clearer, thanks!