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

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Message-ID: <1429158657.7346.160.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 15 Apr 2015 21:30:57 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	stefano.stabellini@...citrix.com, george.dunlap@...citrix.com,
	Jonathan.Davies@...rix.com, xen-devel@...ts.xensource.com,
	wei.liu2@...rix.com, Ian.Campbell@...rix.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	edumazet@...gle.com, paul.durrant@...rix.com,
	christoffer.dall@...aro.org, felipe.franciosi@...rix.com,
	linux-arm-kernel@...ts.infradead.org, david.vrabel@...rix.com
Subject: Re: [Xen-devel] "tcp: refine TSO autosizing" causes performance
 regression on Xen

On Thu, 2015-04-16 at 12:20 +0800, Herbert Xu wrote:
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> > We already have netdev->gso_max_size and netdev->gso_max_segs
> > which are cached into sk->sk_gso_max_size & sk->sk_gso_max_segs
> 
> It is quite dangerous to attempt tricks like this because a
> tc redirection or netfilter nat could change the destination
> device rendering such hints incorrect.

Right but we are talking of performance hints, on quite basic VM setup.

Here the guest would use xen and this hint would apply.




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