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Date: Wed, 20 Nov 2002 22:04:26 +0000
From: Jamie Lokier <lk@tantalophile.demon.co.uk>
To: Davide Libenzi <davidel@xmailserver.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [rfc] epoll interface change and glibc bits ...
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References: <20021120030919.GA9007@bjl1.asuk.net> <Pine.LNX.4.44.0211191957370.1107-100000@blue1.dev.mcafeelabs.com>
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Davide Libenzi wrote:
> And the lower size of the structure will help to reduce the amount of
> memory transfered to userspace. I just saw that adding the extra "obj"
> member lowered performance of about 15% with crazy tests like Ben's
> pipetest. This because it creates, on my machine, more than 400000 events
> per second, and saving memory bandwidth on such conditions is a must. With
> the "more human" http test performance are about the same.

I'd be quite surprised if 400,000 word/sec of memory bandwidth can
explain a 15% time difference, especially considering all the other
things that are done to communicate over a pipe (wakeups etc).

Btw, I have seen variations of that magnitude in other network tests
that I've done that _appear_ to be explained by small changes to the
code like that, but the next day or week the variation stops
correlating with the change.  Page colouring affecting benchmarks
again?

-- Jamie
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