Re: [Xen-devel] [PATCH 00/24] sched: Credit1 and Credit2 improvements... and soft-affinity for Credit2!

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Wed, 2016-08-17 at 19:17 +0200, Dario Faggioli wrote:
> The last 4 patches, still for Credit2, are optimizations, either wrt
> existing
> code, or wrt new code introduced in this series. I've chosen to keep
> them
> separate to make reviewing/understanding new code easier. In fact,
> although
> they look pretty simple, the soft-affinity code was pretty complex
> already, and
> even these simple optimization, if done all at once, would have made
> the
> reviewer's life (unnecessary) tougher.
> 
About this.

I've run the benchmarks with and without these performance optimization
patches, in order to assess their effect as good as I could.

The baseline on top of which I was applying the series is different
from the one used to produce the other numbers reported in the cover
letter, so what's shown there and what I show here is not directly
comparable (but that's not a problem).

Given the nature of the improvements, I've run more iterations of each
configuration of the benchmarks (i.e., 15 iterations instead of 5) to
get more stable results.

Here's my findings:

++++++++++++++++++++++++++++++++++
|    CREDIT1, for reference      |
++++++++++++++++++++++++++++++++++
|               | MAKEXEN IPERF  |
|---------------|----------------|
|no dom0 load   | 28.353  11.793 |
|with dom0 load | 43.955  10.932*|
++++++++++++++++++++++++++++++++++
++++++++++++++++++++++++++++++++++
|   CREDIT2, until patch 20      |
++++++++++++++++++++++++++++++++++
|               | MAKEXEN IPERF  |
|---------------| ---------------|
|no dom0 load   | 28.367  11.716 |
|with dom0 load | 40.591  10.645 |
++++++++++++++++++++++++++++++++++
|+++++++++++++++++++++++++++++++++
|    CREDIT2, full series        |
++++++++++++++++++++++++++++++++++
|               | MAKEXEN IPERF  |
|---------------|----------------|
|no dom0 load   | 27.597* 12.059*|
|with dom0 load | 39.706* 10.609 |
|--------------------------------|

 * marks the best results

So:
 - apart from a glitch on "IPERF with dom0 load", Credit2 with the 
   full series applied is confirmed to be the best. About the glitch:
    - wrt the fact that Credit1 is better, we also have other evidences
      that network throughput could be a bit of a weak spot of Credit2
      versus Credit1 so far (although, we have to admit, they're
      pretty close), and we already have ideas on how to try improve
      the situation;
    - wrt the role played by optimization patches, well, results are
      basically the same.
 - The performance optimization patches do have an (positive!) impact.
 - In case of "no dom0 load, it's actually thanks to the optimization
   patches that Credit2 beats Credit1.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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