netdev - Re: [Xen-devel] [PATCH net-next 2/3] xen-netback: switch to per-cpu scratch space

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Date:	Fri, 24 May 2013 13:31:30 +0100
From:	Wei Liu <wei.liu2@...rix.com>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	Wei Liu <wei.liu2@...rix.com>, <xen-devel@...ts.xen.org>,
	<netdev@...r.kernel.org>, <ian.campbell@...rix.com>,
	<konrad.wilk@...cle.com>
Subject: Re: [Xen-devel] [PATCH net-next 2/3] xen-netback: switch to per-cpu
 scratch space

On Fri, May 24, 2013 at 01:24:41PM +0100, David Vrabel wrote:
> On 24/05/13 11:32, Wei Liu wrote:
> > There are maximum nr_onlie_cpus netback threads running. We can make use of
> > per-cpu scratch space to reduce the size of buffer space when we move to 1:1
> > model.
> 
> How much memory does this actually save?  At first glance the savings
> don't seem worth it for the extra complexity wrt hotplugged VCPUs etc.
> 

It would not save any for the old model netback. But if we switch to 1:1
model the saving depends on how many vifs you run.

This can be calculated by:
(nr_vifs - nr_cpus) * sizeof(scratch space)


Wei.

> David
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