linux-kernel - Re: [PATCH] percpu: add optimized generic percpu accessors

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Message-ID: <20090121100507.GC18728@elte.hu>
Date:	Wed, 21 Jan 2009 11:05:07 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	akpm@...ux-foundation.org, hpa@...or.com, brgerst@...il.com,
	ebiederm@...ssion.com, cl@...ux-foundation.org, travis@....com,
	linux-kernel@...r.kernel.org, steiner@....com, hugh@...itas.com,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Subject: Re: [PATCH] percpu: add optimized generic percpu accessors


* Tejun Heo <tj@...nel.org> wrote:

> Ingo Molnar wrote:
> > The larger point still remains: the kernel dominantly uses static percpu 
> > variables by a margin of 10 to 1, so we cannot just brush away the static 
> > percpu variables and must concentrate on optimizing that side with 
> > priority. It's nice if the dynamic percpu-alloc side improves as well, of 
> > course.
> 
> Well, the infrequent usage of dynamic percpu allocation is in some part 
> due to the poor implementation, so it's sort of chicken and egg problem.  
> I got into this percpu thing because I wanted a percpu reference count 
> which can be dynamically allocated and it sucked.

Sure, but even static percpu sucked very much (it expanded to half a dozen 
or more instructions), and dynamic is _more_ complex. Anyway, it's getting 
fixed now :-)

	Ingo
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