Re: [PATCH] Increase the tx queue to 512 descriptors to fix performance problem.

[Anthony Liguori <anthony-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org>]

Dor Laor wrote:
> On Wed, 2008-01-09 at 08:29 -0600, Anthony Liguori wrote:
>> Dor Laor wrote:
>>> Now that we have a host timer based tx wakeup it waits for 64
>>> packets or timeout before processing them.
>>> This might cause the guest to run out of tx buffers while the host
>>> holds them up.
>>>   
>> There's a proper fix that Rusty added last night.
> 
> This is with his latest patch, without it I got a lot of
> "printk("Unlikely: restart svq failed\n");"
> + The performance is much better now.

How are you getting that?  What are you running and what is your guest 
kernel?  I've not seen that before.


>>> This is a temporal solution to quickly bring back performance to 800mbps.
>>> But a better fix will soon be sent (its not the only problem).
>>>   
>> How are you doing performance testing?
> 
> Not really, this was just to stabilize the module.
> It needs some more work, disable/enable of the device is broken.

What do you mean by disable/enable?  FWIW, your patch really hurts 
netperf performance which is why I asked how you were measuring 800mbps.

Regards,

Anthony Liguori


>> Regards,
>>
>> Anthony Liguori
>>
>>> Signed-off-by: Dor Laor <dor.laor-atKUWr5tajBWk0Htik3J/w@public.gmane.org>
>>> ---
>>>  qemu/hw/virtio-net.c |    2 +-
>>>  1 files changed, 1 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/qemu/hw/virtio-net.c b/qemu/hw/virtio-net.c
>>> index 777fe2c..3d07b65 100644
>>> --- a/qemu/hw/virtio-net.c
>>> +++ b/qemu/hw/virtio-net.c
>>> @@ -293,7 +293,7 @@ void *virtio_net_init(PCIBus *bus, NICInfo *nd, int devfn)
>>>      n->vdev.update_config = virtio_net_update_config;
>>>      n->vdev.get_features = virtio_net_get_features;
>>>      n->rx_vq = virtio_add_queue(&n->vdev, 512, virtio_net_handle_rx);
>>> -    n->tx_vq = virtio_add_queue(&n->vdev, 128, virtio_net_handle_tx);
>>> +    n->tx_vq = virtio_add_queue(&n->vdev, 512, virtio_net_handle_tx);
>>>      n->can_receive = 0;
>>>      memcpy(n->mac, nd->macaddr, 6);
>>>      n->vc = qemu_new_vlan_client(nd->vlan, virtio_net_receive,
>>>   


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