linux-kernel - Re: [PATCH 06/25] hrtimer: Store running timer in hrtimer_clock

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Message-ID: <alpine.DEB.2.20.1709281443570.1879@nanos>
Date:   Thu, 28 Sep 2017 14:45:56 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     Anna-Maria Gleixner <anna-maria@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....org>, keescook@...omium.org,
        John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 06/25] hrtimer: Store running timer in
 hrtimer_clock_base

On Mon, 25 Sep 2017, Peter Zijlstra wrote:

> On Thu, Aug 31, 2017 at 12:23:36PM -0000, Anna-Maria Gleixner wrote:
> > Unfortunately this makes cpu_clock base larger than 32 bytes on 32bit
> > kernels. Instead of having huge gaps due to alignment, remove the alignment
> > and let the compiler pack cpu base for 32bit. The resulting cache access
> > patterns are fortunately not really different from the current
> > behaviour.
> 
> How did you determine this? Perf lacks much useful tooling right about
> there :/

Just by analyzing the resulting layout and looking at the number of cache
lines involved for the frequently used clocks (mono/real).

Thanks,

	tglx