Linux Ethernet Bridging - Mar 2015 - [Bridge] [RFC PATCH v2] bridge: make it possible for packets to traverse the bridge without hitting netfilter

From: Imre Palik <imrep at amazon.de>
Date: Thu, 26 Feb 2015 11:19:25 +0100
> If you are looking for peculiarities in my setup then here they are:
> I am on 4k pages, and perf is not working :-(
> (I am trying to fix those too, but that is far from being a low hanging
fruit.)
> So my guess would be that the packet pipeline doesn't fit in the
cache/tlb
Pure specualtion until you can actually use perf to measure these
things.

And I don't want to apply patches which were designed based upon
pure speculation.

On 02/26/15 17:34, David Miller wrote:
> From: Imre Palik <imrep at amazon.de>
> Date: Thu, 26 Feb 2015 11:19:25 +0100
> 
>> If you are looking for peculiarities in my setup then here they are:
>> I am on 4k pages, and perf is not working :-(
>> (I am trying to fix those too, but that is far from being a low hanging
fruit.)
>> So my guess would be that the packet pipeline doesn't fit in the
cache/tlb
> 
> Pure specualtion until you can actually use perf to measure these
> things.
> 
> And I don't want to apply patches which were designed based upon
> pure speculation.
> 
I did performance measurements in the following way:

Removed those pieces of the packet pipeline that I don't necessarily need
one-by-one.  Then measured their effect on small packet performance.

This was the only part that produced considerable effect.

The pure speculation was about why the effect is more than 15% increase in
packet throughput, although the code path avoided contains way less code than
15% of the packet pipeline.  It seems, Felix Fietkau profiled similar changes,
and found my guess well founded.

Now could anybody explain me what else is wrong with my patch?  I run out of
ideas what to improve.

Thanks

Imre