netdev - Re: [PATCH] percpu: add optimized generic percpu accessors

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Message-Id: <20090121.123420.145043842.davem@davemloft.net>
Date:	Wed, 21 Jan 2009 12:34:20 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	ebiederm@...ssion.com, tj@...nel.org, mingo@...e.hu,
	rusty@...tcorp.com.au, herbert@...dor.apana.org.au,
	akpm@...ux-foundation.org, hpa@...or.com, brgerst@...il.com,
	cl@...ux-foundation.org, travis@....com,
	linux-kernel@...r.kernel.org, steiner@....com, hugh@...itas.com,
	netdev@...r.kernel.org, mathieu.desnoyers@...ymtl.ca
Subject: Re: [PATCH] percpu: add optimized generic percpu accessors

From: Stephen Hemminger <shemminger@...tta.com>
Date: Wed, 21 Jan 2009 23:45:01 +1100

> This is crap. only a small fraction of these SNMP counters are
> close enough to the hot path to deserve per-cpu treatment.

Only if your router/firewall/webserver isn't hitting that code path
which bumps the counters you think aren't hot path.

It's a micro-DoS waiting to happen if we start trying to split
counters up into groups which matter for hot path processing
(and thus use per-cpu stuff) and those which don't (and thus
use atomics or whatever your idea is).
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