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Re: [Xen-devel] Re: [Xen-changelog] Plumb network vif credit-based rate

To: Matt Ayres <matta@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] Re: [Xen-changelog] Plumb network vif credit-based rate limiting thorugh xenbus
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Sat, 1 Apr 2006 17:55:38 +0100
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On 1 Apr 2006, at 17:34, Matt Ayres wrote:

Plumb network vif credit-based rate limiting thorugh xenbus
and xend into xm guest config files.
A new vif parameter 'rate' is supported, with an optional time window
paremeter for specifying granularity of credit replenishment. The default
window is 50ms. For example:
 'rate=10Mb/s'  'rate=250KB/s'  'rate=1MB/s@20ms'

Is this rate in+out or out only? Also, perhaps Chris could explain for us non-kernel hackers the purpose of specifying the credit replenishment granularity and how it can be beneficial to tune it under certain circumstances?

This is out only, but could fairly easily be extended to input too.

Granularity determines the frequency with which the VIFs transmission credit is replenished. So, for example, if you specify 10MB/s@50ms then the VIF is credited with about 50 kilobytes of credit every 50ms. The credit does not accumulate.

A smaller replenishment window will make for slightly less bursty transmission, but there is an overhead as the replenishment rate is increased. Actually we believe that 50ms is a good tradeoff and I wouldn't really expect that anyone would bother to change it.

 -- Keir

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