On 2018年05月08日 11:05, Jason Wang wrote:
Because in virtqueue_enable_cb_delayed(), we may set an
event_off which is bigger than new and both of them have
wrapped. And in this case, although new is smaller than
event_off (i.e. the third param -- old), new shouldn't
add vq->num, and actually we are expecting a very big
idx diff.
Yes, so to calculate distance correctly between event and new, we just
need to compare the warp counter and return false if it doesn't match
without the need to try to add vq.num here.
Thanks
Sorry, looks like the following should work, we need add vq.num if
used_wrap_counter does not match:
static bool vhost_vring_packed_need_event(struct vhost_virtqueue *vq,
__u16 off_wrap, __u16 new,
__u16 old)
{
bool wrap = off_wrap >> 15;
int off = off_wrap & ~(1 << 15);
__u16 d1, d2;
if (wrap != vq->used_wrap_counter)
d1 = new + vq->num - off - 1;
else
d1 = new - off - 1;
if (new > old)
d2 = new - old;
else
d2 = new + vq->num - old;
return d1 < d2;
}
Thanks
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