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

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Date:	Fri, 6 Mar 2015 15:29:32 +0100
From:	Pablo Neira Ayuso <pablo@...filter.org>
To:	Imre Palik <imrep.amz@...il.com>
Cc:	David Miller <davem@...emloft.net>, imrep@...zon.de, 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 Fri, Mar 06, 2015 at 11:34:29AM +0100, Imre Palik wrote:
> 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?

We have to come up with a more generic solution for this.

These sysfs tweaks you're proposing look to me like an obscure way to
tune this.
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