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From: Jesse Gross <jesse@nicira.com>
Date: Mon, 2 May 2011 13:23:38 -0700
Message-ID: <BANLkTimG5fuf9eEzVqsTB_TSy2B1kn5h6g@mail.gmail.com>
Subject: Re: [PATCH] flex_array: avoid divisions when accessing elements
To: Dave Hansen <dave@linux.vnet.ibm.com>
Cc: Eric Paris <eparis@redhat.com>, linux-kernel@vger.kernel.org,
        David Rientjes <rientjes@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
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On Mon, May 2, 2011 at 10:36 AM, Dave Hansen <dave@linux.vnet.ibm.com> wrote:
> On Mon, 2011-05-02 at 13:26 -0400, Eric Paris wrote:
>> On most architectures division is an expensive operation and accessing an
>> element currently requires four of them. ?This performance penalty
>> effectively precludes flex arrays from being used on any kind of fast
>> path. ?However, two of these divisions can be handled at creation time and
>> the others can be replaced by a reciprocal divide, completely avoiding
>> real divisions on access.
>>
>> Signed-off-by: Jesse Gross <jesse@nicira.com>
>> Cc: David Rientjes <rientjes@google.com>
>> Cc: Eric Paris <eparis@redhat.com>
>> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
>> [rebase on top of changes to support 0 len elements: eparis]
>> [initialize part_nr when array fits entirely in base: eparis]
>> Signed-off-by: Eric Paris <eparis@redhat.com>
>
> This seems sane to me, especially in the element access case.
>
> Acked-by: Dave Hansen <dave@linux.vnet.ibm.com>

Thanks Eric!
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