netdev - Re: [PATCH v7 0/8] Request for inclusion: tcp memory buffers

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Message-ID: <4E9746B0.7030603@parallels.com>
Date:	Fri, 14 Oct 2011 00:14:40 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	David Miller <davem@...emloft.net>
CC:	<linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
	<lizf@...fujitsu.com>, <kamezawa.hiroyu@...fujitsu.com>,
	<ebiederm@...ssion.com>, <paul@...lmenage.org>,
	<gthelen@...gle.com>, <netdev@...r.kernel.org>,
	<linux-mm@...ck.org>, <kirill@...temov.name>,
	<avagin@...allels.com>, <devel@...nvz.org>
Subject: Re: [PATCH v7 0/8] Request for inclusion: tcp memory buffers

On 10/14/2011 12:12 AM, David Miller wrote:
> From: Glauber Costa<glommer@...allels.com>
> Date: Fri, 14 Oct 2011 00:05:58 +0400
>
>> Also, I kind of dispute the affirmation that !cgroup will encompass
>> the majority of users, since cgroups is being enabled by default by
>> most vendors. All systemd based systems use it extensively, for
>> instance.
>
> I will definitely advise people against this, since the cost of having
> this on by default is absolutely non-trivial.
>
> People keep asking every few releases "where the heck has my performance
> gone" and it's because of creeping features like this.  This socket
> cgroup feature is a prime example of where that kind of stuff comes
> from.
>
> I really get irritated when people go "oh, it's just one indirect
> function call" and "oh, it's just one more pointer in struct sock"
>
> We work really hard to _remove_ elements from structures and make them
> smaller, and to remove expensive operations from the fast paths.
>
> It might take someone weeks if not months to find a way to make a
> patch which compensates for the extra overhead your patches are adding.
>
> And I don't think you fully appreciate that.

Let's focus on this:
Are you happy, or at least willing to accept, an approach that keep 
things as they were with cgroups *compiled out*, or were you referring 
to not in use == compiled in, but with no users?

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