netdev - Re: [RFC] [PATCH] Optimize TCP sendmsg in favour of fast devices?

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Message-ID: <OF0A3AFFAB.FFA8088C-ON652576B1.001D7B08-652576B1.0042980B@in.ibm.com>
Date:	Wed, 20 Jan 2010 17:49:18 +0530
From:	Krishna Kumar2 <krkumar2@...ibm.com>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, ilpo.jarvinen@...sinki.fi,
	netdev@...r.kernel.org
Subject: Re: [RFC] [PATCH] Optimize TCP sendmsg in favour of fast devices?

Hi Dave,

> David Miller <davem@...emloft.net> wrote on 01/15/2010 02:48:29 PM:
>
> Re: [RFC] [PATCH] Optimize TCP sendmsg in favour of fast devices?
>
> From: Krishna Kumar2 <krkumar2@...ibm.com>
> Date: Fri, 15 Jan 2010 14:50:04 +0530
>
> > I wonder if there is some other way to test it. I could test it on
> > the card I have, cxgbe, by ethtool F_SG off, and then testing
> > this patch with existing code (both with ethtool F_SG off)? Will
> > that be enough to get an idea, or I cannot assume this is
> > reasonable for real non-sg drivers? I am sure there is a
> > degradation, and mentioned that part as a "penalty" for those
> > drivers in my patch.
>
> I think such a test would provide useful data by which to judge this
> change.

I had to remove the F_SG flag from cxgb3 driver (using ethtool
didn't show any difference in performance since GSO was enabled
on the device due to register_netdev setting it). Testing show a
drop of 25% in performance with this patch for non-SG device,
the extra alloc/memcpy is showing up.

For the SG driver, I get a good performace gain (not anywhere
close to 25% though). What do you suggest?

Thanks,

- KK

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