Re: [dpdk-stable] [PATCH v2] vhost: fix assuming packed ring size is a power of 2

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

Hi Cheng,

Thanks for catching the issue.
It was an accident, that I thought I had resolved already :)

This is fixed now.

Maxime

On 7/12/21 8:53 AM, Jiang, Cheng1 wrote:
> Hi Maxime,
> 
> I have noticed you changed the state this patch to Superseded.
> So are you going to submit a new version of this patch?
> 
> Thanks,
> Cheng
> 
>> -----Original Message-----
>> From: Jiang, Cheng1
>> Sent: Wednesday, July 7, 2021 7:11 PM
>> To: Maxime Coquelin <maxime.coquelin@redhat.com>; dev@dpdk.org; Xia,
>> Chenbo <Chenbo.Xia@intel.com>
>> Cc: stable@dpdk.org
>> Subject: RE: [PATCH v2] vhost: fix assuming packed ring size is a power of 2
>>
>> Hi Maxime,
>>
>> I have also noticed the wrong calculation here, thanks for the timely help.
>>
>> Thanks,
>> Cheng
>>
>>> -----Original Message-----
>>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
>>> Sent: Wednesday, July 7, 2021 6:30 PM
>>> To: dev@dpdk.org; Jiang, Cheng1 <cheng1.jiang@intel.com>; Xia, Chenbo
>>> <chenbo.xia@intel.com>
>>> Cc: Maxime Coquelin <maxime.coquelin@redhat.com>; stable@dpdk.org
>>> Subject: [PATCH v2] vhost: fix assuming packed ring size is a power of
>>> 2
>>>
>>> Unlike split ring, packed ring does not mandate the ring size to be a
>>> power of 2. So we have to use a modulo operation when wrapping ring
>> index.
>>>
>>> Fixes: 873e8dad6f49 ("vhost: support packed ring in async datapath")
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>>> ---
>>>
>>> V2: Also fix wrapping in virtio_dev_rx_async_get_info_idx which is
>>> used in the packed ring data path.
>>>
>>>  lib/vhost/virtio_net.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/vhost/virtio_net.c b/lib/vhost/virtio_net.c index
>>> b93482587c..0de5231db7 100644
>>> --- a/lib/vhost/virtio_net.c
>>> +++ b/lib/vhost/virtio_net.c
>>> @@ -1470,7 +1470,7 @@ virtio_dev_rx_async_get_info_idx(uint16_t
>>> pkts_idx,
>>>  	uint16_t vq_size, uint16_t n_inflight)  {
>>>  	return pkts_idx > n_inflight ? (pkts_idx - n_inflight) :
>>> -		(vq_size - n_inflight + pkts_idx) & (vq_size - 1);
>>> +		(vq_size - n_inflight + pkts_idx) % vq_size;
>>>  }
>>>
>>>  static __rte_always_inline void
>>> @@ -2131,7 +2131,7 @@ uint16_t rte_vhost_poll_enqueue_completed(int
>>> vid, uint16_t queue_id,
>>>
>>>  	if (vq_is_packed(dev)) {
>>>  		for (i = 0; i < n_pkts_put; i++) {
>>> -			from = (start_idx + i) & (vq_size - 1);
>>> +			from = (start_idx + i) % vq_size;
>>>  			n_buffers += pkts_info[from].nr_buffers;
>>>  			pkts[i] = pkts_info[from].mbuf;
>>>  		}
>>> --
>>> 2.31.1
>>
>>
>> Acked-by: Cheng Jiang <cheng1.jiang@intel.com>
>