netdev - Re: [PATCH] virtio_net: suppress cpu stall when free_unused

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Date:   Thu, 27 Apr 2023 15:02:26 +0800
From:   Wenliang Wang <wangwenliang.1995@...edance.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc:     virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, mst@...hat.com, jasowang@...hat.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com
Subject: Re: [PATCH] virtio_net: suppress cpu stall when free_unused_bufs



On 4/27/23 2:20 PM, Xuan Zhuo wrote:
> On Thu, 27 Apr 2023 12:34:33 +0800, Wenliang Wang <wangwenliang.1995@...edance.com> wrote:
>> For multi-queue and large rx-ring-size use case, the following error
> 
> Cound you give we one number for example?

128 queues and 16K queue_size is typical.

> 
>> occurred when free_unused_bufs:
>> rcu: INFO: rcu_sched self-detected stall on CPU.
>>
>> Signed-off-by: Wenliang Wang <wangwenliang.1995@...edance.com>
>> ---
>>   drivers/net/virtio_net.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index ea1bd4bb326d..21d8382fd2c7 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -3565,6 +3565,7 @@ static void free_unused_bufs(struct virtnet_info *vi)
>>   		struct virtqueue *vq = vi->rq[i].vq;
>>   		while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
>>   			virtnet_rq_free_unused_buf(vq, buf);
>> +		schedule();
> 
> Just for rq?
> 
> Do we need to do the same thing for sq?
Rq buffers are pre-allocated, take seconds to free rq unused buffers.

Sq unused buffers are much less, so do the same for sq is optional.

> 
> Thanks.
> 
> 
>>   	}
>>   }
>>
>> --
>> 2.20.1
>>