netdev - Re: [PATCH net-next v8 7/7] net: vhost: make busyloop_intr more accurate

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Date:   Tue, 21 Aug 2018 08:47:35 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     xiangxia.m.yue@...il.com, mst@...hat.com,
        makita.toshiaki@....ntt.co.jp
Cc:     netdev@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH net-next v8 7/7] net: vhost: make busyloop_intr more
 accurate

On 2018年08月21日 08:33, Jason Wang wrote:
>
>
> On 2018年08月19日 20:11, xiangxia.m.yue@...il.com wrote:
>> From: Tonghao Zhang <xiangxia.m.yue@...il.com>
>>
>> The patch uses vhost_has_work_pending() to check if
>> the specified handler is scheduled, because in the most case,
>> vhost_has_work() return true when other side handler is added
>> to worker list. Use the vhost_has_work_pending() insead of
>> vhost_has_work().
>>
>> Topology:
>> [Host] ->linux bridge -> tap vhost-net ->[Guest]
>>
>> TCP_STREAM (netperf):
>> * Without the patch:  38035.39 Mbps, 3.37 us mean latency
>> * With the patch:     38409.44 Mbps, 3.34 us mean latency
>
> The improvement is not obvious as last version. Do you imply there's 
> some recent changes of vhost that make it faster?
>

I misunderstood the numbers, please ignore this.

It shows less than 1% improvement. I'm not sure it's worth to do so. Can 
you try bi-directional pktgen to see if it has more obvious effect?

Thanks

> Thanks
>
>>
>> Signed-off-by: Tonghao Zhang <xiangxia.m.yue@...il.com>
>> ---
>>   drivers/vhost/net.c | 9 ++++++---
>>   1 file changed, 6 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index db63ae2..b6939ef 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -487,10 +487,8 @@ static void vhost_net_busy_poll(struct vhost_net 
>> *net,
>>       endtime = busy_clock() + busyloop_timeout;
>>         while (vhost_can_busy_poll(endtime)) {
>> -        if (vhost_has_work(&net->dev)) {
>> -            *busyloop_intr = true;
>> +        if (vhost_has_work(&net->dev))
>>               break;
>> -        }
>>             if ((sock_has_rx_data(sock) &&
>>                !vhost_vq_avail_empty(&net->dev, rvq)) ||
>> @@ -513,6 +511,11 @@ static void vhost_net_busy_poll(struct vhost_net 
>> *net,
>>           !vhost_has_work_pending(&net->dev, VHOST_NET_VQ_RX))
>>           vhost_net_enable_vq(net, rvq);
>>   +    if (vhost_has_work_pending(&net->dev,
>> +                   poll_rx ?
>> +                   VHOST_NET_VQ_RX: VHOST_NET_VQ_TX))
>> +        *busyloop_intr = true;
>> +
>>       mutex_unlock(&vq->mutex);
>>   }
>
> _______________________________________________
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> Virtualization@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization

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