netdev - Re: [Xen-devel] [PATCHv1] xen-netfront: always keep the Rx ring full of requests

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Message-Id: <542D7361020000780003C014@mail.emea.novell.com>
Date:	Thu, 02 Oct 2014 14:46:41 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"David Vrabel" <david.vrabel@...rix.com>
Cc:	<xen-devel@...ts.xenproject.org>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	<netdev@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCHv1] xen-netfront: always keep the Rx
 ring full of requests

>>> On 02.10.14 at 15:33, <david.vrabel@...rix.com> wrote:
> A full Rx ring only requires 1 MiB of memory.  This is not enough
> memory that it is useful to dynamically scale the number of Rx
> requests in the ring based on traffic rates.

The performance benefits are nice, but does the above statement
scale to hundreds of guests with perhaps multiple NICs and/or
queues?

Jan

> Keeping the ring full of Rx requests handles bursty traffic better
> than trying to converges on an optimal number of requests to keep
> filled.
> 
> On a 4 core host, an iperf -P 64 -t 60 run from dom0 to a 4 VCPU guest
> improved from 5.1 Gbit/s to 5.6 Gbit/s.  Gains with more bursty
> traffic are expected to be higher.
> 
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>


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