Messages in this thread | | | Subject | Re: [RFC v3 3/5] virtio_ring: add packed ring support | From | Jason Wang <> | Date | Thu, 10 May 2018 15:34:50 +0800 |
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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
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