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

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Date:	Thu, 15 Jan 2009 12:32:30 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
Cc:	roel kluin <roel.kluin@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Brian Gerst <brgerst@...il.com>,
	ebiederm@...ssion.com, cl@...ux-foundation.org,
	rusty@...tcorp.com.au, travis@....com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	steiner@....com, hugh@...itas.com
Subject: Re: [patch] add optimized generic percpu accessors


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

> roel kluin wrote:
> >> Index: linux/include/asm-generic/percpu.h
> >> ===================================================================
> >> --- linux.orig/include/asm-generic/percpu.h
> >> +++ linux/include/asm-generic/percpu.h
> >> @@ -80,4 +80,32 @@ extern void setup_per_cpu_areas(void);
> >>  #define DECLARE_PER_CPU(type, name) extern PER_CPU_ATTRIBUTES \
> >>                                        __typeof__(type) per_cpu_var(name)
> >>
> >> +/*
> >> + * Optional methods for optimized non-lvalue per-cpu variable access:
> >> + */
> >> +
> >> +#ifndef percpu_read
> >> +# define percpu_read(var)              __get_cpu_var(var)
> >> +#endif
> >> +
> >> +#ifndef percpu_write
> >> +# define percpu_write(var, val)                ({ __get_cpu_var(var) = (val); })
> >> +#endif
> >> +
> >> +#ifndef percpu_add
> >> +# define percpu_add(var, val)          ({ __get_cpu_var(var) += (val); })
> >> +#endif
> >> +
> >> +#ifndef percpu_sub
> >> +# define percpu_add(var, val)          ({ __get_cpu_var(var) += (val); })
> > 
> > this should be:
> > 
> > define percpu_sub(var, val)          ({ __get_cpu_var(var) -= (val); })

well spotted!

> Thanks.  Will fold into the patch.

thanks!

Is there any interim tree for us to pull into -tip? I'd rather not let 
this grow too big, it will be harder and harder to debug any regressions. 
Gradual progress is a lot more debuggable. Your initial patchset is 
fantastic already (gives a ~0.2% kernel image size saving for defconfig), 
so it's a very good start.

	Ingo
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