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

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Date:	Thu, 13 Oct 2011 16:12:21 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	glommer@...allels.com
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

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.
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