Messages in this thread | | | Subject | Re: [RFC v3 3/5] virtio_ring: add packed ring support | From | Jason Wang <> | Date | Thu, 10 May 2018 15:32:19 +0800 |
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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
c) id = 4,count = 2,next_avail = 0
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
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