Subject: Re: memset (was: Redundant memset in AIO read_events)
From: Arjan van de Ven <arjanv@redhat.com>
Reply-To: arjanv@redhat.com
To: Etienne Lorrain <etienne_lorrain@yahoo.fr>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <20030710100417.83333.qmail@web11801.mail.yahoo.com>
References: <20030710100417.83333.qmail@web11801.mail.yahoo.com>
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Organization: Red Hat, Inc.
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Date: 10 Jul 2003 12:19:21 +0200
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On Thu, 2003-07-10 at 12:04, Etienne Lorrain wrote:
>  Note that using memset() is better reserved to initialise variable-size
>  structures or buffers. Even if memset() is extremely optimised,
>  it is still not as fast as not doing anything.

this is not always true....
memset can be used as an optimized cache-warmup, which can avoid the
write-allocate behavior of normal writes, which means that if you memset
a structure first and then fill it, it can be halve the memory bandwidth
and thus half as fast. This assumes an optimized memset which we
*currently* don't have I think... but well, we can fix that ;)


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