From: "Michael S. Tsirkin" <mst@redhat.com>
To: "Xie, Huawei" <huawei.xie@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
Stephen Hemminger <stephen@networkplumber.org>,
Tetsuya Mukawa <mukawa@igel.co.jp>,
"Traynor, Kevin" <kevin.traynor@intel.com>,
"Tan, Jianfeng" <jianfeng.tan@intel.com>,
Yuanhan Liu <yuanhan.liu@linux.intel.com>
Subject: Re: [dpdk-dev] [RFC PATCH] avail idx update optimizations
Date: Sun, 24 Apr 2016 12:15:36 +0300 [thread overview]
Message-ID: <20160424120551-mutt-send-email-mst@redhat.com> (raw)
In-Reply-To: <C37D651A908B024F974696C65296B57B4C7199DC@SHSMSX101.ccr.corp.intel.com>
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++;
> >> }
> >>
> >
>
next prev parent reply other threads:[~2016-04-24 9:15 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-21 17:18 Huawei Xie
[not found] ` <C37D651A908B024F974696C65296B57B4C713327@SHSMSX101.ccr.corp.intel.com>
2016-04-24 2:45 ` Xie, Huawei
2016-04-24 9:15 ` Michael S. Tsirkin [this message]
2016-04-24 13:23 ` Xie, Huawei
2016-04-28 9:17 ` Xie, Huawei
2016-04-27 8:53 ` [dpdk-dev] [PATCH] virtio: avoid avail ring entry index update if equal Huawei Xie
2016-04-28 6:19 ` Yuanhan Liu
2016-04-28 8:14 ` Thomas Monjalon
2016-04-28 13:15 ` Xie, Huawei
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