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

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Message-ID: <CAFLBxZarvxtq-6fNAxioq64bw6SMZFVuoLzJgK=E6nvcbS2X4w@mail.gmail.com>
Date:	Mon, 20 Apr 2015 12:03:02 +0100
From:	George Dunlap <George.Dunlap@...citrix.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	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>,
	Daniel Borkmann <daniel@...earbox.net>,
	Stefano Stabellini <stefano.stabellini@...citrix.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

On Thu, Apr 16, 2015 at 1:42 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Thu, 2015-04-16 at 11:01 +0100, George Dunlap wrote:
>
>> He suggested that after he'd been prodded by 4 more e-mails in which two
>> of us guessed what he was trying to get at.  That's what I was
>> complaining about.
>
> My big complain is that I suggested to test to double the sysctl, which
> gave good results.
>
> Then you provided a patch using a 8x factor. How does that sound ?
>
> Next time I ask a raise, I should try a 8x factor as well, who knows,
> it might be accepted.

I see.  I chose the value that Stefano had determined had completely
eliminated the overhead.  Doubling the value reduces the overhead to
8%, which should be fine for a short-term fix while we git a proper
mid/long-term fix.

 -George
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