From: "Michael S. Tsirkin" <mst@redhat.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: dev@dpdk.org, i.maximets@samsung.com, tiwei.bie@intel.com,
zhihong.wang@intel.com, jfreiman@redhat.com
Subject: Re: [dpdk-dev] [PATCH v3] vhost: batch used descs chains write-back with packed ring
Date: Thu, 20 Dec 2018 09:30:30 -0500 [thread overview]
Message-ID: <20181220092201-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20181220100022.3531-1-maxime.coquelin@redhat.com>
On Thu, Dec 20, 2018 at 11:00:22AM +0100, Maxime Coquelin wrote:
> Instead of writing back descriptors chains in order, let's
> write the first chain flags last in order to improve batching.
>
> With Kernel's pktgen benchmark, ~3% performance gain is measured.
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
> lib/librte_vhost/virtio_net.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c
> index 8c657a101..66ccd3c35 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -97,6 +97,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
> {
> int i;
> uint16_t used_idx = vq->last_used_idx;
> + uint16_t head_idx = vq->last_used_idx;
> + uint16_t head_flags = 0;
>
> /* Split loop in two to save memory barriers */
> for (i = 0; i < vq->shadow_used_idx; i++) {
> @@ -126,12 +128,17 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
> flags &= ~VRING_DESC_F_AVAIL;
> }
>
> - vq->desc_packed[vq->last_used_idx].flags = flags;
> + if (i > 0) {
> + vq->desc_packed[vq->last_used_idx].flags = flags;
>
> - vhost_log_cache_used_vring(dev, vq,
> + vhost_log_cache_used_vring(dev, vq,
> vq->last_used_idx *
> sizeof(struct vring_packed_desc),
> sizeof(struct vring_packed_desc));
> + } else {
> + head_idx = vq->last_used_idx;
> + head_flags = flags;
> + }
>
> vq->last_used_idx += vq->shadow_used_packed[i].count;
> if (vq->last_used_idx >= vq->size) {
> @@ -140,7 +147,15 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
> }
> }
>
> + vq->desc_packed[head_idx].flags = head_flags;
> +
> rte_smp_wmb();
> +
> + vhost_log_cache_used_vring(dev, vq,
> + head_idx *
> + sizeof(struct vring_packed_desc),
> + sizeof(struct vring_packed_desc));
> +
> vq->shadow_used_idx = 0;
> vhost_log_cache_sync(dev, vq);
How about moving rte_smp_wmb into logging functions?
This way it's free with log disabled even on arm...
> }
> --
> 2.17.2
next prev parent reply other threads:[~2018-12-20 14:30 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-20 10:00 Maxime Coquelin
2018-12-20 10:07 ` Tiwei Bie
2018-12-20 14:30 ` Michael S. Tsirkin [this message]
2018-12-20 15:32 ` Maxime Coquelin
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