Message-ID: <1429158657.7346.160.camel@edumazet-glaptop2.roam.corp.google.com>
Subject: Re: [Xen-devel] "tcp: refine TSO autosizing" causes performance
 regression on Xen
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Herbert Xu <herbert@gondor.apana.org.au>
Cc: stefano.stabellini@eu.citrix.com, george.dunlap@eu.citrix.com,
        Jonathan.Davies@citrix.com, xen-devel@lists.xensource.com,
        wei.liu2@citrix.com, Ian.Campbell@citrix.com, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, edumazet@google.com,
        paul.durrant@citrix.com, christoffer.dall@linaro.org,
        felipe.franciosi@citrix.com, linux-arm-kernel@lists.infradead.org,
        david.vrabel@citrix.com
Date: Wed, 15 Apr 2015 21:30:57 -0700
In-Reply-To: <20150416042005.GA12179@gondor.apana.org.au>
References: <20150416042005.GA12179@gondor.apana.org.au>
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On Thu, 2015-04-16 at 12:20 +0800, Herbert Xu wrote:
> Eric Dumazet <eric.dumazet@gmail.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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