Re: [Qemu-devel] [Bug 1066055] Re: Network performance regression with vde_switch

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Oct 15, 2012 at 09:46:06PM -0000, Edivaldo de Araujo Pereira wrote:
> Hi Stefan,
> 
> Thank you, very much for taking the time to help me, and excuse me for
> not seeing your answer early...
> 
> I've run the procedure you pointed me out, and the result is:
> 
> 0d8d7690850eb0cf2b2b60933cf47669a6b6f18f is the first bad commit
> commit 0d8d7690850eb0cf2b2b60933cf47669a6b6f18f
> Author: Amit Shah <amit.shah@redhat.com>
> Date:   Tue Sep 25 00:05:15 2012 +0530
> 
>     virtio: Introduce virtqueue_get_avail_bytes()
> 
>     The current virtqueue_avail_bytes() is oddly named, and checks if a
>     particular number of bytes are available in a vq.  A better API is to
>     fetch the number of bytes available in the vq, and let the caller do
>     what's interesting with the numbers.
> 
>     Introduce virtqueue_get_avail_bytes(), which returns the number of bytes
>     for buffers marked for both, in as well as out.  virtqueue_avail_bytes()
>     is made a wrapper over this new function.
> 
>     Signed-off-by: Amit Shah <amit.shah@redhat.com>
>     Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> 
> :040000 040000 1a58b06a228651cf844621d9ee2f49b525e36c93
> e09ea66ce7f6874921670b6aeab5bea921a5227d M      hw
> 
> I tried to revert that patch in the latest version, but it obviously
> didnt work; I'm trying to figure out the problem, but I don't know very
> well the souce code, so I think it's going to take some time. For now,
> it's all I could do.
> 
> Thank you, again.
> Edivaldo


Could you please try reverting the following two patches:
git revert 0d8d7690850eb0cf2b2b60933cf47669a6b6f18f
git revert ad3005ad8c70a69705149d3ce6d1e51fb76edb15

the result will build and will confirm that this is the problem.

Amit, could you please clarify what kind of performance
gain if any do you see from ad3005ad8c70a69705149d3ce6d1e51fb76edb15?

If it's small maybe we should simply revert?

-- 
MST