Date: Sat, 23 Sep 2006 08:38:33 +0100 From: David Malone <dwmalone@maths.tcd.ie> To: Robert Watson <rwatson@FreeBSD.org> Cc: Andre Oppermann <andre@FreeBSD.org>, Andrew Gallatin <gallatin@cs.duke.edu>, alc@FreeBSD.org, freebsd-net@FreeBSD.org, freebsd-current@FreeBSD.org, tegge@FreeBSD.org Subject: Re: Much improved sendfile(2) kernel implementation Message-ID: <20060923073833.GA10269@walton.maths.tcd.ie> In-Reply-To: <20060922234708.V11343@fledge.watson.org> References: <4511B9B1.2000903@freebsd.org> <17683.63162.919620.114649@grasshopper.cs.duke.edu> <45145F1D.8020005@freebsd.org> <20060922234708.V11343@fledge.watson.org>
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On Fri, Sep 22, 2006 at 11:48:23PM +0100, Robert Watson wrote: > The impact of TSO is clearly dramatic, especially when combined with the > patch, but I'm a bit concerned by the drop in performance in the patched > non-TSO case. For network cards which will always have TSO enabled, this > isn't an issue, but do we see a similar affect for drivers without TSO? > What can we put this drop down to? We probably also need to make sure that any performance increase in TSO isn't due to us getting TCP congestion control wrong. I think in Linux they had problems when they first introduced TSO because TCP was advancing the congestion window by a TSO-sized chunk instead of a wire packet. OTOH, I think Andre and Drew's tests are low-latency, so congestion control isn't likely to be playing a big role, so the improvements are unlikely to be due to this. David.
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