netdev - Re: [PATCH net V2] vhost_net: correctly check tx avail during rx busy polling

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Message-Id: <20170905.144804.755338183074090970.davem@davemloft.net>
Date:   Tue, 05 Sep 2017 14:48:04 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jasowang@...hat.com
Cc:     mst@...hat.com, netdev@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net V2] vhost_net: correctly check tx avail during rx
 busy polling

From: Jason Wang <jasowang@...hat.com>
Date: Tue,  5 Sep 2017 09:22:05 +0800

> We check tx avail through vhost_enable_notify() in the past which is
> wrong since it only checks whether or not guest has filled more
> available buffer since last avail idx synchronization which was just
> done by vhost_vq_avail_empty() before. What we really want is checking
> pending buffers in the avail ring. Fix this by calling
> vhost_vq_avail_empty() instead.
> 
> This issue could be noticed by doing netperf TCP_RR benchmark as
> client from guest (but not host). With this fix, TCP_RR from guest to
> localhost restores from 1375.91 trans per sec to 55235.28 trans per
> sec on my laptop (Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz).
> 
> Fixes: 030881372460 ("vhost_net: basic polling support")
> Signed-off-by: Jason Wang <jasowang@...hat.com>

Applied and queued up for -stable, thanks.