linux-kernel - Re: [PATCH 02/16] virtio_ring: virtqueue_add

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Message-ID: <20130226093030.GA21763@redhat.com>
Date:	Tue, 26 Feb 2013 11:30:30 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Paolo Bonzini <pbonzini@...hat.com>, Asias He <asias@...hat.com>,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 02/16] virtio_ring: virtqueue_add_sgs, to add multiple
 sgs.

On Tue, Feb 26, 2013 at 03:44:26PM +1030, Rusty Russell wrote:
> "Michael S. Tsirkin" <mst@...hat.com> writes:
> > On Tue, Feb 19, 2013 at 06:26:20PM +1030, Rusty Russell wrote:
> >> virtio_scsi can really use this, to avoid the current hack of copying
> >> the whole sg array.  Some other things get slightly neater, too.
> >> 
> >> Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
> >
> > Hmm, this makes add_buf a bit slower. virtio_test results
> > (I'll send a patch to update the test shortly):
> >
> > Before:
> > 0.09user 0.01system 0:00.12elapsed 91%CPU (0avgtext+0avgdata 480maxresident)k
> > 0inputs+0outputs (0major+145minor)pagefaults 0swaps
> >
> > After:
> > 0.11user 0.01system 0:00.13elapsed 90%CPU (0avgtext+0avgdata 480maxresident)k
> > 0inputs+0outputs (0major+145minor)pagefaults 0swaps
> 
> Interesting: how much of this is due to the shim in virtqueue_add_buf()
> to clean up the sg arrays?
> 
> (Perhaps we should make virtio_test run for longer, too).
> 
> BTW, you might be interested in:
>         https://github.com/rustyrussell/stats.git
> 
> Which provides a useful filter for multiple results.
> 
> Cheers,
> Rusty.

Nifty.
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