From: Jim Nance <jlnance@sdf.lonestar.org>
Date: Sun, 22 Jan 2006 14:24:01 +0000
To: Jon Smirl <jonsmirl@gmail.com>
Cc: lkml <linux-kernel@vger.kernel.org>
Subject: Re: sendfile() with 100 simultaneous 100MB files
Message-ID: <20060122142401.GA24738@SDF.LONESTAR.ORG>
References: <9e4733910601201353g36284133xf68c4f6eae1344b4@mail.gmail.com>
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On Fri, Jan 20, 2006 at 04:53:44PM -0500, Jon Smirl wrote:

> Any other ideas why sendfile() would get into a seek storm?

I can't really comment on the quality of the linux sendfile() implementation,
I've never looked at the code.  However, a couple of general observations.

The seek storm happens because linux is trying to be "fair," where fair
means no one process get to starve another for I/O bandwidth.

The fastest way to transfer 100 100M files would be to send them one at a
time.  The 99th person in line of course would percieve this as a very poor
implementation.  The current sendfile implementation seems to live at the
other end of the extream.

It is possible to come up with a compromise behavior by limiting the
number of concurrent sendfiles running, and the maximum size they are
allowed to send in one squirt.

Thanks,

Jim

-- 
jlnance@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org
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