linux-kernel - Re: [tip:x86/mm] percpu: Introduce a read-mostly percpu API

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Date:	Thu, 21 Oct 2010 09:38:33 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	"hpa@...or.com" <hpa@...or.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"hpa@...ux.intel.com" <hpa@...ux.intel.com>
Subject: Re: [tip:x86/mm] percpu: Introduce a read-mostly percpu API

Hi hpa,
On Thu, Oct 21, 2010 at 07:06:59AM +0800, tip-bot for Shaohua Li wrote:
> [ hpa: moved it *after* the page-aligned section, for obvious
>   reasons. ]
move it after page-aligned section can't guarantee to avoid cache false sharing.
we need:
. = ALIGN(CACHE_LINE_SIZE);
*(.data..percpu..readmostly)
. = ALIGN(CACHE_LINE_SIZE);
To make sure before/after readmostly section doesn't share cache line with
others. The headcache is some arch need L1_CACHE_SIZE and others need
(1 << INTERNODE_CACHE_SHIFT). We need change all ARCHs to make this happen.
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