netdev - Re: [RFC PATCH v2] bridge: make it possible for packets to traverse the bridge without hitting netfilter

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Date:	Fri, 06 Mar 2015 11:34:29 +0100
From:	Imre Palik <imrep.amz@...il.com>
To:	David Miller <davem@...emloft.net>, imrep@...zon.de
CC:	fw@...len.de, bridge@...ts.linux-foundation.org,
	stephen@...workplumber.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, aliguori@...zon.com, nbd@...nwrt.org
Subject: Re: [RFC PATCH v2] bridge: make it possible for packets to traverse
 the bridge without hitting netfilter

On 02/26/15 17:34, David Miller wrote:
> From: Imre Palik <imrep@...zon.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
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