netdev - Re: Network performance with small packets

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Message-ID: <20110309171603.GD7165@redhat.com>
Date:	Wed, 9 Mar 2011 19:16:03 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Shirley Ma <mashirle@...ibm.com>
Cc:	Tom Lendacky <tahm@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Krishna Kumar2 <krkumar2@...ibm.com>,
	David Miller <davem@...emloft.net>, kvm@...r.kernel.org,
	netdev@...r.kernel.org, steved@...ibm.com
Subject: Re: Network performance with small packets - continued

On Wed, Mar 09, 2011 at 08:51:33AM -0800, Shirley Ma wrote:
> On Wed, 2011-03-09 at 10:09 -0600, Tom Lendacky wrote:
> > > > Vhost is receiving a lot of notifications for packets that are to
> > be
> > > > transmitted (over 60% of the packets generate a kick_notify). 
> 
> This is guest TX send notification when vhost enables notification.
> 
> In TCP_STREAM test, vhost exits from reaching NAPI WEIGHT,


You mean virtio?

> it rarely
> enables the notification, vhost re-enters handle_tx from NAPI poll,

Does NAPI really call handle_tx? Not rx?

> so
> guest doesn't do much kick_notify.
> 
> In multiple TCP_RR test, seems vhost exits from nothing to send in TX vq
> very often, so it enables notification most of the time.
> 
> Shirley
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