netdev - Re: [PATCH vhost] vhost_net: Fix too many vring kick on busypoll

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Date:   Mon, 2 Jul 2018 11:59:42 +0900
From:   Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Jason Wang <jasowang@...hat.com>, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org
Subject: Re: [PATCH vhost] vhost_net: Fix too many vring kick on busypoll

On 2018/06/30 1:38, Michael S. Tsirkin wrote:
...
>> Performance numbers:
>>
>> - Bulk transfer from guest to external physical server.
>>     [Guest]->vhost_net->tap--(XDP_REDIRECT)-->i40e --(wire)--> [Server]
>> - Set 10us busypoll.
>> - Guest disables checksum and TSO because of host XDP.
>> - Measured single flow Mbps by netperf, and kicks by perf kvm stat
>>   (EPT_MISCONFIG event).
>>
>>                             Before              After
>>                           Mbps  kicks/s      Mbps  kicks/s
>> UDP_STREAM 1472byte              247758                 27
>>                 Send   3645.37            6958.10
>>                 Recv   3588.56            6958.10
>>               1byte                9865                 37
>>                 Send      4.34               5.43
>>                 Recv      4.17               5.26
>> TCP_STREAM             8801.03    45794   9592.77     2884
>>
>> Signed-off-by: Toshiaki Makita <makita.toshiaki@....ntt.co.jp>
> 
> Is this with busy poll enabled?

Yes, as I wrote "Set 10us busypoll" above.

> Are there CPU utilization #s?

I used one cpu for one vcpu and one cpu for one vhost.
Each host cpu for vcpu/vhost was like this:

- Before
 vcpu cpu : %guest 70 %sys 30
 vhost cpu: %sys 100

- After
 vcpu cpu : %guest 100
 vhost cpu: %sys 100

I think %sys before patch was caused by vring kick.

-- 
Toshiaki Makita