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From: Tiwei Bie <tiwei.bie@intel.com>
To: Maxime Coquelin <maxime.coquelin@redhat.com>
Cc: dev@dpdk.org, jfreimann@redhat.com, zhihong.wang@intel.com,
	stable@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v2] vhost: avoid memory barriers when no descriptors dequeued
Date: Wed, 24 Oct 2018 16:50:24 +0800	[thread overview]
Message-ID: <20181024085024.GA4708@debian> (raw)
In-Reply-To: <20181023100710.14739-1-maxime.coquelin@redhat.com>

On Tue, Oct 23, 2018 at 12:07:10PM +0200, 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(-)

Reviewed-by: Tiwei Bie <tiwei.bie@intel.com>

  parent reply	other threads:[~2018-10-24  8:51 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-23 10:07 Maxime Coquelin
2018-10-23 12:39 ` [dpdk-dev] [dpdk-stable] " Jens Freimann
2018-10-24  8:50 ` Tiwei Bie [this message]
2018-10-24 10:51 ` [dpdk-dev] " Maxime Coquelin

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