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SubjectRe: [PATCH 6/6] vhost_net: don't poll on -EFAULT
On 04/16/2012 03:16 PM, Michael S. Tsirkin wrote:
> On Mon, Apr 16, 2012 at 02:08:33PM +0800, Jason Wang wrote:
>> Currently, we restart tx polling unconditionally when sendmsg()
>> fails. This would cause unnecessary wakeups of vhost wokers as it's
>> only needed when the socket send buffer were exceeded.
> Why is this a problem?

This issue is when guest driver is able to hit the -EFAULT, vhost
discard the the descriptor and restart the polling. This would wake
vhost thread and repeat the loop again which waste cpu.

Another possible solution is don't discard the descriptor.
>
>> Fix this by
>> restart the tx polling only when sendmsg() returns value other than
>> -EFAULT.
>>
>> Signed-off-by: Jason Wang<jasowang@redhat.com>
>> ---
>> drivers/vhost/net.c | 3 ++-
>> 1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index 29abd65..035fa95 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -262,7 +262,8 @@ static void handle_tx(struct vhost_net *net)
>> UIO_MAXIOV;
>> }
>> vhost_discard_vq_desc(vq, 1);
>> - tx_poll_start(net, sock);
>> + if (err != -EFAULT)
>> + tx_poll_start(net, sock);
>> break;
>> }
>> if (err != len)
> --
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