[Qemu-devel] Re: [PATCH v5 0/4] virtio: Use ioeventfd for virtqueue notify

[Stefan Hajnoczi]

On Sun, Dec 12, 2010 at 9:09 PM, Michael S. Tsirkin <address@hidden> wrote:
> On Sun, Dec 12, 2010 at 10:56:34PM +0200, Michael S. Tsirkin wrote:
>> On Sun, Dec 12, 2010 at 10:42:28PM +0200, Michael S. Tsirkin wrote:
>> > On Sun, Dec 12, 2010 at 10:41:28PM +0200, Michael S. Tsirkin wrote:
>> > > On Sun, Dec 12, 2010 at 03:02:04PM +0000, Stefan Hajnoczi wrote:
>> > > > See below for the v5 changelog.
>> > > >
>> > > > Due to lack of connectivity I am sending from GMail.  Git should 
>> > > > retain my
>> > > > address@hidden From address.
>> > > >
>> > > > Virtqueue notify is currently handled synchronously in userspace 
>> > > > virtio.  This
>> > > > prevents the vcpu from executing guest code while hardware emulation 
>> > > > code
>> > > > handles the notify.
>> > > >
>> > > > On systems that support KVM, the ioeventfd mechanism can be used to 
>> > > > make
>> > > > virtqueue notify a lightweight exit by deferring hardware emulation to 
>> > > > the
>> > > > iothread and allowing the VM to continue execution.  This model is 
>> > > > similar to
>> > > > how vhost receives virtqueue notifies.
>> > > >
>> > > > The result of this change is improved performance for userspace virtio 
>> > > > devices.
>> > > > Virtio-blk throughput increases especially for multithreaded scenarios 
>> > > > and
>> > > > virtio-net transmit throughput increases substantially.
>> > >
>> > > Interestingly, I see decreased throughput for small message
>> > > host to get netperf runs.
>> > >
>> > > The command that I used was:
>> > > netperf -H $vguest -- -m 200
>> > >
>> > > And the results are:
>> > > - with ioeventfd=off
>> > > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.104 
>> > > (11.0.0.104) port 0 AF_INET : demo
>> > > Recv   Send    Send                          Utilization       Service 
>> > > Demand
>> > > Socket Socket  Message  Elapsed              Send     Recv     Send    
>> > > Recv
>> > > Size   Size    Size     Time     Throughput  local    remote   local   
>> > > remote
>> > > bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   
>> > > us/KB
>> > >
>> > >  87380  16384    200    10.00      3035.48   15.50    99.30    6.695   
>> > > 2.680
>> > >
>> > > - with ioeventfd=on
>> > > TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.104 
>> > > (11.0.0.104) port 0 AF_INET : demo
>> > > Recv   Send    Send                          Utilization       Service 
>> > > Demand
>> > > Socket Socket  Message  Elapsed              Send     Recv     Send    
>> > > Recv
>> > > Size   Size    Size     Time     Throughput  local    remote   local   
>> > > remote
>> > > bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   
>> > > us/KB
>> > >
>> > >  87380  16384    200    10.00      1770.95   18.16    51.65    13.442  
>> > > 2.389
>> > >
>> > >
>> > > Do you see this behaviour too?
>> >
>> > Just a note: this is with the patchset ported to qemu-kvm.
>>
>> And just another note: the trend is reversed for larged messages,
>> e.g. with 1.5k messages ioeventfd=on outputforms ioeventfd=off.
>
> Another datapoint where I see a regression is with 4000 byte messages
> for guest to host traffic.
>
> ioeventfd=off
> set_up_server could not establish a listen endpoint for  port 12865 with 
> family AF_UNSPEC
> TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.4 (11.0.0.4) 
> port 0 AF_INET : demo
> Recv   Send    Send                          Utilization       Service Demand
> Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
> Size   Size    Size     Time     Throughput  local    remote   local   remote
> bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB
>
>  87380  16384   4000    10.00      7717.56   98.80    15.11    1.049   2.566
>
> ioeventfd=on
> TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 11.0.0.4 (11.0.0.4) 
> port 0 AF_INET : demo
> Recv   Send    Send                          Utilization       Service Demand
> Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
> Size   Size    Size     Time     Throughput  local    remote   local   remote
> bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB
>
>  87380  16384   4000    10.00      3965.86   87.69    15.29    1.811   5.055

Interesting.  I posted the following results in an earlier version of
this patch:

"Sridhar Samudrala <address@hidden> collected the following data for
virtio-net with 2.6.36-rc1 on the host and 2.6.34 on the guest.

Guest to Host TCP_STREAM throughput(Mb/sec)
-------------------------------------------
Msg Size  vhost-net  virtio-net  virtio-net/ioeventfd
65536         12755        6430                  7590
16384          8499        3084                  5764
 4096          4723        1578                  3659"

Here we got a throughput improvement where you got a regression.  Your
virtio-net ioeventfd=off throughput is much higher than what we got
(different hardware and configuration, but still I didn't know that
virtio-net reaches 7 Gbit/s!).

I have focussed on the block side of things.  Any thoughts about the
virtio-net performance we're seeing?

" 1024          1827         981                  2060

Host to Guest TCP_STREAM throughput(Mb/sec)
-------------------------------------------
Msg Size  vhost-net  virtio-net  virtio-net/ioeventfd
65536         11156        5790                  5853
16384         10787        5575                  5691
 4096         10452        5556                  4277
 1024          4437        3671                  5277

Guest to Host TCP_RR latency(transactions/sec)
----------------------------------------------

Msg Size  vhost-net  virtio-net  virtio-net/ioeventfd
   1          9903        3459                  3425
 4096          7185        1931                  1899
16384          6108        2102                  1923
65536          3161        1610                  1744"

I'll also run the netperf tests you posted to check what I get.

Stefan