Re: [dpdk-dev] [PATCH] vhost: Clean iotlb cache on vring stop

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 9/23/21 10:48, Xia, Chenbo wrote:
> Hi Maxime,
> 
>> -----Original Message-----
>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>> Sent: Thursday, September 23, 2021 4:34 PM
>> To: Eugenio Pérez <eperezma@redhat.com>; Xia, Chenbo <chenbo.xia@intel.com>
>> Cc: dev@dpdk.org; Pei Zhang <pezhang@redhat.com>; Jason Wang
>> <jasowang@redhat.com>
>> Subject: Re: [PATCH] vhost: Clean iotlb cache on vring stop
>>
>>
>>
>> On 8/27/21 18:12, Eugenio Pérez wrote:
>>> Old IOVA cache entries are left when there is a change on virtio driver
>>> in VM. In case that all these old entries have iova addresses lesser
>>> than new iova entries, vhost code will need to iterate all the cache to
>>> find the new ones. In case of just a new iova entry needed for the new
>>> translations, this condition will last forever.
>>>
>>> This has been observed in virtio-net to testpmd's vfio-pci driver
>>> transition, reducing the performance from more than 10Mpps to less than
>>> 0.07Mpps if the hugepage address was higher than the networking
>>> buffers. Since all new buffers are contained in this new gigantic page,
>>> vhost needs to scan IOTLB_CACHE_SIZE - 1 for each translation at worst.
>>>
>>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
>>> Reported-by: Pei Zhang <pezhang@redhat.com>
>>> ---
>>>    lib/vhost/vhost_user.c | 2 ++
>>>    1 file changed, 2 insertions(+)
>>>
>>> diff --git a/lib/vhost/vhost_user.c b/lib/vhost/vhost_user.c
>>> index 29a4c9af60..7de48f5333 100644
>>> --- a/lib/vhost/vhost_user.c
>>> +++ b/lib/vhost/vhost_user.c
>>> @@ -2113,6 +2113,8 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
>>>    	msg->size = sizeof(msg->payload.state);
>>>    	msg->fd_num = 0;
>>>
>>> +	vhost_user_iotlb_flush_all(vq);
>>> +
>>>    	vring_invalidate(dev, vq);
>>>
>>>    	return RTE_VHOST_MSG_RESULT_REPLY;
>>>
>>
>> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> 
> So you will fix title and add fix tag when applying, right?

Yes, I will. Thanks for the heads-up!

Maxime

> /Chenbo
> 
>>
>> Thanks,
>> Maxime
>