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

From: George Dunlap <[email-masked]>
Date: Thu, 16 Apr 2015 09:56:22 +0100

On 04/15/2015 07:19 PM, Eric Dumazet wrote:
> On Wed, 2015-04-15 at 19:04 +0100, George Dunlap wrote:
> 
>> Maybe you should stop wasting all of our time and just tell us what
>> you're thinking.
> 
> I think you make me wasting my time.
> 
> I already gave all the hints in prior discussions.

Right, and I suggested these two options:

"Obviously one solution would be to allow the drivers themselves to set
the tcp_limit_output_bytes, but that seems like a maintenance
nightmare.

"Another simple solution would be to allow drivers to indicate whether
they have a high transmit latency, and have the kernel use a higher
value by default when that's the case." [1]

Neither of which you commented on.  Instead you pointed me to a comment
that only partially described what the limitations were. (I.e., it
described the "two packets or 1ms", but not how they related, nor how
they related to the "max of 2 64k packets outstanding" of the default
tcp_limit_output_bytes setting.)

 -George

[1]
http://marc.info/?i=<CAFLBxZYt7-v29ysm=[email-masked]>