lkml.org 
[lkml]   [2018]   [May]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC v3 3/5] virtio_ring: add packed ring support
From
Date


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

\
 
 \ /
  Last update: 2018-05-10 09:32    [W:0.118 / U:0.392 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site