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

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Date:	Wed, 18 Nov 2015 17:21:15 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Marc Gonzalez <marc_gonzalez@...madesigns.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mans Rullgard <mans@...sr.com>,
	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

On Wed, Nov 18, 2015 at 02:43:34PM +0100, Marc Gonzalez wrote:
> 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. A nice side-effect
> of this patch is making container_of() unnecessary, which makes the
> code a bit simpler.
> 
> On 32-bit platforms, reg fits in the padding between read and mask,
> meaning no downside from storing it there.

Just swap the order of 'reg' and 'clksrc'.

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