linux-kernel - Re: Loopback and Nagle's algorithm

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Message-ID: <BANLkTi=jpdLRc35DkBhLmUr8-P+ggcrgoA@mail.gmail.com>
Date:	Tue, 12 Apr 2011 10:45:19 +0100
From:	Will Newton <will.newton@...il.com>
To:	Adam McLaurin <lkml@...tas.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Loopback and Nagle's algorithm

On Tue, Apr 12, 2011 at 3:37 AM, Adam McLaurin <lkml@...tas.net> wrote:
> I understand that disabling Nagle's algorithm via TCP_NODELAY will
> generally degrade throughput. However, in my scenario (150 byte
> messages, sending as fast as possible), the actual throughput penalty
> over the network is marginal (maybe 10% at most).
>
> However, when I disable Nagle's algorithm when connecting over loopback,
> the performance hit is *huge* - 10x reduction in throughput.
>
> The question is, why is disabling Nagle's algorithm on loopback so much
> worse w.r.t. throughput? Is there anything I can do to reduce the
> incurred throughput penalty?

It may be caused by an increase in context switch rate, as both sender
and receiver are on the same machine.
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