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

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Date:	Tue, 26 Feb 2013 15:44:26 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
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.

"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.
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