Re: [PATCH net v2 2/2] vhost_net: fix high cpu load when sendmsg fails

[Jason Wang <jasowang@redhat.com>]

On 2020/12/22 上午7:07, Willem de Bruijn wrote:
> On Wed, Dec 16, 2020 at 3:20 AM wangyunjian<wangyunjian@huawei.com>  wrote:
>> From: Yunjian Wang<wangyunjian@huawei.com>
>>
>> Currently we break the loop and wake up the vhost_worker when
>> sendmsg fails. When the worker wakes up again, we'll meet the
>> same error.
> The patch is based on the assumption that such error cases always
> return EAGAIN. Can it not also be ENOMEM, such as from tun_build_skb?
>
>> This will cause high CPU load. To fix this issue,
>> we can skip this description by ignoring the error. When we
>> exceeds sndbuf, the return value of sendmsg is -EAGAIN. In
>> the case we don't skip the description and don't drop packet.
> the -> that
>
> here and above: description -> descriptor
>
> Perhaps slightly revise to more explicitly state that
>
> 1. in the case of persistent failure (i.e., bad packet), the driver
> drops the packet
> 2. in the case of transient failure (e.g,. memory pressure) the driver
> schedules the worker to try again later


If we want to go with this way, we need a better time to wakeup the 
worker. Otherwise it just produces more stress on the cpu that is what 
this patch tries to avoid.

Thanks


>
>