linux-kernel - Re: [Xen-devel] "tcp: refine TSO autosizing" causes performance regression on Xen

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Message-ID: <20150416130043.GL13443@deinos.phlegethon.org>
Date:	Thu, 16 Apr 2015 14:00:43 +0100
From:	Tim Deegan <tim@....org>
To:	George Dunlap <george.dunlap@...citrix.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Jonathan Davies <Jonathan.Davies@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	netdev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Paul Durrant <paul.durrant@...rix.com>,
	linux-arm-kernel@...ts.infradead.org,
	Felipe Franciosi <felipe.franciosi@...rix.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [Xen-devel] "tcp: refine TSO autosizing" causes performance
 regression on Xen

At 12:39 +0100 on 16 Apr (1429187952), George Dunlap wrote:
> Your comment lists three benefits:
> 1. better RTT estimation
> 2. faster recovery
> 3. high rates
> 
> #3 is just marketing fluff; it's also contradicted by the statement that
> immediately follows it -- i.e., there are drivers for which the
> limitation does *not* give high rates.

AFAICT #3 is talking about throughput _under TCP_, where inflating the
RTT will absolutely cause problems.

Tim.
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