linux-kernel - Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

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Message-ID: <y2k84144f021005102342m18bce930g53599c9112565f78@mail.gmail.com>
Date:	Tue, 11 May 2010 09:42:03 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Mike Frysinger <vapier.adi@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oskar Schirmer <os@...ix.com>,
	Michael Hennerich <Michael.Hennerich@...log.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	Daniel Glöckner <dg@...ix.com>,
	Oliver Schneidewind <osw@...ix.com>,
	Johannes Weiner <jw@...ix.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines

Hi Dmitry,

On Tue, May 11, 2010 at 9:33 AM, Dmitry Torokhov
<dmitry.torokhov@...il.com> wrote:
>> what guarantee exactly do you have for that statement ?
>
> The data is kmalloced, kmalloc aligns on cacheline boundary AFAIK which
> means that next kmalloc data chunk will not share "our" cacheline.

No, there are no such guarantees. kmalloc() aligns on
ARCH_KMALLOC_MINALIGN or ARCH_SLAB_MINALIGN depending on which is
bigger but beyond that, there are no guarantees. You can, of course,
use kmem_cache_create() with SLAB_HWCACHE_ALIGN to align on cacheline
boundary.

                        Pekka
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