linux-kernel - Re: [PATCH] clocksource: Store reg field within struct clocksource

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Message-ID: <yw1xvb8zfmbb.fsf@unicorn.mansr.com>
Date:	Wed, 18 Nov 2015 13:51:04 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Marc Gonzalez <marc_gonzalez@...madesigns.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Russell King <linux@....linux.org.uk>,
	LKML <linux-kernel@...r.kernel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Nicolas Pitre <nico@...aro.org>,
	Tony Lindgren <tony@...mide.com>,
	Sebastian Frias <sebastian_frias@...madesigns.com>
Subject: Re: [PATCH] clocksource: Store reg field within struct clocksource

Marc Gonzalez <marc_gonzalez@...madesigns.com> writes:

> Since 'struct clocksource' is ____cacheline_aligned, gcc must insert
> a lot of padding between reg and clksrc in 'struct clocksource_mmio'
> (for example, L1_CACHE_BYTES = 64 on ARMv7).
>
> Storing reg within 'struct clocksource' removes unnecessary padding,
> and reg can then be grouped with other hot data.

Can you demonstrate a difference with this change?  Not saying it's bad,
but it's always good to have numbers.

> A nice side-effect of this patch is making container_of() unnecessary,
> which makes the code a bit simpler.

You really need to get used to that construct.

-- 
Måns Rullgård
mans@...sr.com
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