netdev - Re: Performance regression on kernels 3.10 and newer

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Message-ID: <1408049466.6804.40.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 14 Aug 2014 13:51:06 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	Rick Jones <rick.jones2@...com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: Performance regression on kernels 3.10 and newer

On Thu, 2014-08-14 at 13:31 -0700, Alexander Duyck wrote:

> My concern here is that netperf is a standard tool to use for testing
> network performance, and the kernel default is to run with
> tcp_low_latency disabled.  As such the prequeue is a part of the
> standard path is it not?  If the prequeue isn't really useful anymore
> should we consider pulling it out of the kernel, or disabling it by
> making tcp_low_latency the default?

Feel free to use netperf, but please do not complain if linux kernel is
not optimized for netperf, using a 20 years old application design (one
thread per flow)

prequeue only works when few TCP flows are active.

For dozen of active flows, then you probably need some tweaks,
like the ones in Documentation/networking/scaling.txt

Then, prequeue or not, you would not notice.


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