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

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Date:	Thu, 21 Oct 2010 08:48:05 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Shaohua Li <shaohua.li@...el.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...hat.com" <mingo@...hat.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

Le jeudi 21 octobre 2010 à 14:17 +0800, Shaohua Li a écrit :
> This isn't a previous bug. see
> #define DECLARE_PER_CPU_PAGE_ALIGNED(type, name)			\
> 	DECLARE_PER_CPU_SECTION(type, name, "..page_aligned")		\
> 	__aligned(PAGE_SIZE)
> the ..page_aligned is already page aligned. I add it is because it can make
> the .readmostly section guarantee to have no cache false sharing, because
> I add the . = ALIGN(PAGE_SIZE); before .readmostly section, and .page_aligned
> follows, but for sure this wates some memory.

A small note:

The __aligned(XXX) makes sure object _starts_ at XXX boundary, not that
following one will also use same alignment. Of course, we can argue that
we dont try to put in PAGE_ALIGNED section small objects, but still...

Explicit .ALIGN() uses in .lds are more readable IMHO...



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