linux-kernel - Re: [PATCH 2/2] virtio_net: Improve the recv buffer allocation scheme

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Message-ID: <20081009153546.GA6912@sequoia.sous-sol.org>
Date:	Thu, 9 Oct 2008 08:35:46 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Mark McLoughlin <markmc@...hat.com>, virtualization@...ts.osdl.org,
	linux-kernel@...r.kernel.org, Herbert Xu <herbert.xu@...hat.com>
Subject: Re: [PATCH 2/2] virtio_net: Improve the recv buffer allocation
	scheme

* Rusty Russell (rusty@...tcorp.com.au) wrote:
> On Thursday 09 October 2008 06:34:59 Mark McLoughlin wrote:
> > From: Herbert Xu <herbert.xu@...hat.com>
> >
> > If segmentation offload is enabled by the host, we currently allocate
> > maximum sized packet buffers and pass them to the host. This uses up
> > 20 ring entries, allowing us to supply only 20 packet buffers to the
> > host with a 256 entry ring. This is a huge overhead when receiving
> > small packets, and is most keenly felt when receiving MTU sized
> > packets from off-host.
> 
> There are three approaches we should investigate before adding YA feature.  
> Obviously, we can simply increase the number of ring entries.

Tried that, it didn't help much.  I don't have my numbers handy, but
levelled off at about 512 and was a modest boost.  It's still wasteful
to preallocate like that on the off-chance it's a large packet.

thanks,
-chris
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