netdev - Re: Network performance with small packets

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Date:	Tue, 01 Feb 2011 22:05:48 -0800
From:	Shirley Ma <mashirle@...ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Sridhar Samudrala <sri@...ibm.com>,
	Steve Dobbelstein <steved@...ibm.com>,
	David Miller <davem@...emloft.net>, kvm@...r.kernel.org,
	mashirle@...ux.vnet.ibm.com, netdev@...r.kernel.org
Subject: Re: Network performance with small packets

On Wed, 2011-02-02 at 06:40 +0200, Michael S. Tsirkin wrote:
> ust tweak the parameters with sysfs, you do not have to edit the code:
> echo 64 > /sys/module/vhost_net/parameters/tx_bufs_coalesce
> 
> Or in a similar way for tx_packets_coalesce (since we use indirect,
> packets will typically use 1 buffer each).

We should use packets instead of buffers, in indirect case, one packet
has multiple buffers, each packet uses one descriptor from the ring
(default size is 256).

echo 128 > /sys/module/vhost_net/parameters/tx_packets_coalesce

The way I am changing is only when netif queue has stopped, then we
start to count num_free descriptors to send the signal to wake netif
queue.

Shirley

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