linux-kernel - Re: [Xen-devel] "tcp: refine TSO autosizing" causes performance regression on Xen

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Date:	Wed, 15 Apr 2015 11:19:15 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	George Dunlap <george.dunlap@...citrix.com>,
	Jonathan Davies <Jonathan.Davies@...rix.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Wei Liu <wei.liu2@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	netdev <netdev@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Paul Durrant <paul.durrant@...rix.com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Felipe Franciosi <felipe.franciosi@...rix.com>,
	linux-arm-kernel@...ts.infradead.org,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [Xen-devel] "tcp: refine TSO autosizing" causes performance regression
 on Xen

On 04/15/2015 11:08 AM, Eric Dumazet wrote:
> On Wed, 2015-04-15 at 10:55 -0700, Rick Jones wrote:
>>>
>>> Have you tested this patch on a NIC without GSO/TSO ?
>>>
>>> This would allow more than 500 packets for a single flow.
>>>
>>> Hello bufferbloat.
>>
>> Woudln't the fq_codel qdisc on that interface address that problem?
>
> Last time I checked, default qdisc was pfifo_fast.

Bummer.

> These guys do not want to change a sysctl, how pfifo_fast will magically
> becomes fq_codel ?

Well, I'm not sure that it is George and Jonathan themselves who don't 
want to change a sysctl, but the customers who would have to tweak that 
in their VMs?

rick
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