linux-kernel - Re: [PATCH] hrtimer: Replace cpu_base->active_bases with a direct check of the active list

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Message-ID: <alpine.DEB.2.11.1504091054410.3845@nanos>
Date:	Thu, 9 Apr 2015 10:58:16 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ingo Molnar <mingo@...nel.org>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Ingo Molnar <mingo@...hat.com>, linaro-kernel@...ts.linaro.org,
	linux-kernel@...r.kernel.org,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Subject: Re: [PATCH] hrtimer: Replace cpu_base->active_bases with a direct
 check of the active list

On Thu, 9 Apr 2015, Ingo Molnar wrote:
> Plus, look at this code in hrtimer_run_queues():
> 
>         for (index = 0; index < HRTIMER_MAX_CLOCK_BASES; index++) {
>                 base = &cpu_base->clock_base[index];
>                 if (!base->active.next)
>                         continue;
> 
>                 if (gettime) {
>                         hrtimer_get_softirq_time(cpu_base);
>                         gettime = 0;
>                 }
> 
> if at least one base is active (on my fairly standard system all cpus 
> have at least one active hrtimer base all the time - and many cpus 
> have two bases active), then we run hrtimer_get_softirq_time(), which 
> dirties the cachelines of all 4 clock bases:
> 
>         base->clock_base[HRTIMER_BASE_REALTIME].softirq_time = xtim;
>         base->clock_base[HRTIMER_BASE_MONOTONIC].softirq_time = mono;
>         base->clock_base[HRTIMER_BASE_BOOTTIME].softirq_time = boot;
>         base->clock_base[HRTIMER_BASE_TAI].softirq_time = tai;

This is the non highres case and we actually could optimize that case
as well to avoid the cache line polution.

Thanks,

	tglx



 
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