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Message-ID: <9e4733910603182010p394c3233p81825b093fb693c@mail.gmail.com>
Date: Sat, 18 Mar 2006 23:10:33 -0500
From: "Jon Smirl" <jonsmirl@gmail.com>
To: "Wu Fengguang" <wfg@mail.ustc.edu.cn>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 00/23] Adaptive read-ahead V11
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On 3/18/06, Wu Fengguang <wfg@mail.ustc.edu.cn> wrote:
> On Sat, Mar 18, 2006 at 10:10:43PM -0500, Jon Smirl wrote:
> > This is probably a readahead problem. The lighttpd people that are
> > encountering this problem are not regular lkml readers.
> >
> > http://bugzilla.kernel.org/show_bug.cgi?id=5949
>
> [QUOTE]
>         My general conclusion is that since they were able to write a user
>         space implementation that avoids the problem something must be broken
>         in the kernel readahead logic for sendfile().
>
> Maybe the user space solution does the trick by using a larger window size?
>
> IMHO, the stock read-ahead is not designed with extremely high concurrency in
> mind. However, 100 streams should not be a problem at all.

Has anyone checked to see if the readahead logic is working as
expected from sendfile? IO from sendfile is a different type of
context than IO from user space, there could be sendfile specific
problems. If window size is the trick, shouldn't sendfile
automatically adapt it's window size? I don't think you can control
the sendfile window size from user space.

The goal of sendfile is to be the most optimal way to send a file over
the network. This is a case where user space code is easily beating
it.

--
Jon Smirl
jonsmirl@gmail.com
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