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From: Jason Wang <jasowang@redhat.com>
To: Tiwei Bie <tiwei.bie@intel.com>,
	mst@redhat.com, virtualization@lists.linux-foundation.org,
	linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Cc: wexu@redhat.com
Subject: Re: [RFC v3 3/5] virtio_ring: add packed ring support
Date: Thu, 10 May 2018 15:34:50 +0800	[thread overview]
Message-ID: <5885acac-e9e3-3abf-b6a2-7347f4d55be2@redhat.com> (raw)
In-Reply-To: <927f4478-5a81-31d4-ac69-f9ec26248591@redhat.com>



On 2018年05月10日 15:32, Jason Wang wrote:
>
>
> On 2018年04月25日 13:15, Tiwei Bie wrote:
>> +    /* We're using some buffers from the free list. */
>> +    vq->vq.num_free -= descs_used;
>> +
>> +    /* Update free pointer */
>> +    if (indirect) {
>> +        n = head + 1;
>> +        if (n >= vq->vring_packed.num) {
>> +            n = 0;
>> +            vq->wrap_counter ^= 1;
>> +        }
>> +        vq->next_avail_idx = n;
>> +    } else
>> +        vq->next_avail_idx = i;
>
> During testing zerocopy (out of order completion), I found driver may 
> submit two identical buffer id to vhost. So the above code may not 
> work well.
>
> Consider the case that driver adds 3 buffer and virtqueue size is 8.
>
> a) id = 0,count = 2,next_avail = 2
>
> b) id = 2,count = 4,next_avail = 2

next_avail should be 6 here.

>
> c) id = 4,count = 2,next_avail = 0
>

id should be 6 here.

Thanks

> if packet b is done before packet a, driver may think buffer id 0 is 
> available and try to use it if even if the real buffer 0 was not done.
>
> Thanks
> _______________________________________________
> Virtualization mailing list
> Virtualization@lists.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/virtualization

  reply	other threads:[~2018-05-10  7:34 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-25  5:15 [RFC v3 0/5] virtio: support packed ring Tiwei Bie
2018-04-25  5:15 ` [RFC v3 1/5] virtio: add packed ring definitions Tiwei Bie
2018-04-25  5:15 ` [RFC v3 2/5] virtio_ring: support creating packed ring Tiwei Bie
2018-04-25  5:15 ` [RFC v3 3/5] virtio_ring: add packed ring support Tiwei Bie
2018-05-10  7:32   ` Jason Wang
2018-05-10  7:34     ` Jason Wang [this message]
2018-05-10  8:56       ` Tiwei Bie
2018-05-10  9:49         ` Jason Wang
2018-05-10 10:50           ` Tiwei Bie
2018-04-25  5:15 ` [RFC v3 4/5] virtio_ring: add event idx support in packed ring Tiwei Bie
2018-05-02  2:51   ` Jason Wang
2018-05-02  7:28     ` Tiwei Bie
2018-05-02 13:51       ` Michael S. Tsirkin
2018-05-02 15:12         ` Tiwei Bie
2018-05-02 15:42           ` Michael S. Tsirkin
2018-05-03  1:11             ` Tiwei Bie
2018-05-03  1:44               ` Michael S. Tsirkin
2018-05-03  2:09                 ` Tiwei Bie
2018-05-03  7:25                   ` Jason Wang
2018-05-03 13:54                     ` Tiwei Bie
2018-05-08  3:05                       ` Jason Wang
2018-05-08  5:40                         ` Jason Wang
2018-05-08  6:44                           ` Tiwei Bie
2018-05-08  7:16                             ` Jason Wang
2018-05-08  9:16                               ` Tiwei Bie
2018-05-08  9:34                                 ` Jason Wang
2018-05-08  9:44                                   ` Tiwei Bie
2018-05-09  3:43                                     ` Jason Wang
2018-05-16  5:01   ` Jason Wang
2018-05-16  5:55     ` Tiwei Bie
2018-04-25  5:15 ` [RFC v3 5/5] virtio_ring: enable " Tiwei Bie
2018-04-27  3:56 ` [RFC v3 0/5] virtio: support " Jason Wang
2018-04-27  4:18   ` Michael S. Tsirkin
2018-04-27  6:17     ` Jason Wang
2018-04-27  9:12       ` Tiwei Bie
2018-04-28  2:45         ` Jason Wang
2018-05-02  3:49 ` Jason Wang

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