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From: Maxime Coquelin <maxime.coquelin@redhat.com>
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(mx1.redhat.com [10.5.110.39]); Wed, 24 Oct 2018 10:51:56 +0000 (UTC)
Subject: Re: [dpdk-stable] [PATCH v2] vhost: avoid memory barriers when no
descriptors dequeued
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On 10/23/18 12:07 PM, Maxime Coquelin wrote:
> In both split and packed dequeue paths, flush_shadow_used_ring
> and vhost_ring_call variants gets called even if not packets
> have been dequeued, and so no descriptors updates happened.
>
> It has an impact on CPU pipeline, as memory barriers are used
> in these functions.
>
> This patch don't call these functions if no descriptors have
> been dequeued. The performance gain with split ring when
> dequeue zero-copy is disabled should be null, but should be
> noticeable with packed ring or dequeue zero-copy enabled.
>
> Fixes: ae999ce49dcb ("vhost: add Tx support for packed ring")
> Fixes: 915cf9404225 ("vhost: use shadow used ring in dequeue path")
> Cc:stable@dpdk.org
>
> Signed-off-by: Maxime Coquelin<maxime.coquelin@redhat.com>
> ---
>
> Changes in v2:
> - Fix shadow_used_idx reset in error path (Tiwei)
>
> lib/librte_vhost/virtio_net.c | 24 ++++++++++++++++--------
> 1 file changed, 16 insertions(+), 8 deletions(-)
Applied to dpdk-next-virtio/master.
Maxime