On Sun, Apr 24, 2016 at 02:45:22AM +0000, Xie, Huawei wrote: > Forget to cc the mailing list. > > On 4/22/2016 9:53 PM, Xie, Huawei wrote: > > Hi: > > > > This is a series of virtio/vhost idx/ring update optimizations for cache > > to cache transfer. Actually I don't expect many of them as virtio/vhost > > has already done quite right.
Hmm - is it a series or a single patch? > > For this patch, in a VM2VM test, i observed ~6% performance increase. Interesting. In that case, it seems likely that new ring layout would give you an even bigger performance gain. Could you take a look at tools/virtio/ringtest/ring.c in latest Linux and tell me what do you think? In particular, I know you looked at using vectored instructions to do ring updates - would the layout in tools/virtio/ringtest/ring.c interfere with that? > > In VM1, run testpmd with txonly mode > > In VM2, run testpmd with rxonly mode > > In host, run testpmd(with two vhostpmds) with io forward > > > > Michael: > > We have talked about this method when i tried the fixed ring. > > > > > > On 4/22/2016 5:12 PM, Xie, Huawei wrote: > >> eliminate unnecessary cache to cache transfer between virtio and vhost > >> core Yes I remember proposing this, but you probably should include the explanation about why this works in he commit log: - pre-format avail ring with expected descriptor index values - as long as entries are consumed in-order, there's no need to modify the avail ring - as long as avail ring is not modified, it can be valid in caches of both consumer and producer > >> > >> --- > >> drivers/net/virtio/virtqueue.h | 3 ++- > >> 1 file changed, 2 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/net/virtio/virtqueue.h > >> b/drivers/net/virtio/virtqueue.h > >> index 4e9239e..8c46a83 100644 > >> --- a/drivers/net/virtio/virtqueue.h > >> +++ b/drivers/net/virtio/virtqueue.h > >> @@ -302,7 +302,8 @@ vq_update_avail_ring(struct virtqueue *vq, uint16_t > >> desc_idx) > >> * descriptor. > >> */ > >> avail_idx = (uint16_t)(vq->vq_avail_idx & (vq->vq_nentries - 1)); > >> - vq->vq_ring.avail->ring[avail_idx] = desc_idx; > >> + if (unlikely(vq->vq_ring.avail->ring[avail_idx] != desc_idx)) > >> + vq->vq_ring.avail->ring[avail_idx] = desc_idx; > >> vq->vq_avail_idx++; > >> } > >> > > >
