linux-kernel - Re: [PATCH] percpu: convert SNMP mibs to new infra

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Date:	Fri, 3 Apr 2009 19:10:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Eric Dumazet <dada1@...mosbay.com>
Cc:	Tejun Heo <htejun@...il.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] percpu: convert SNMP mibs to new infra


* Eric Dumazet <dada1@...mosbay.com> wrote:

> Ingo Molnar a écrit :
> > * Tejun Heo <htejun@...il.com> wrote:
> > 
> >> Hello, Eric, Ingo.
> >>
> >> Eric Dumazet wrote:
> >>> diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
> >>> index aee103b..6b82f6b 100644
> >>> --- a/arch/x86/include/asm/percpu.h
> >>> +++ b/arch/x86/include/asm/percpu.h
> >>> @@ -135,6 +135,9 @@ do {							\
> >>>  #define percpu_read(var)	percpu_from_op("mov", per_cpu__##var)
> >>>  #define percpu_write(var, val)	percpu_to_op("mov", per_cpu__##var, val)
> >>>  #define percpu_add(var, val)	percpu_to_op("add", per_cpu__##var, val)
> >>> +#define indir_percpu_add(var, val)	percpu_to_op("add", *(var), val)
> >>> +#define indir_percpu_inc(var)       percpu_to_op("add", *(var), 1)
> >>> +#define indir_percpu_dec(var)       percpu_to_op("add", *(var), -1)
> >>>  #define percpu_sub(var, val)	percpu_to_op("sub", per_cpu__##var, val)
> >>>  #define percpu_and(var, val)	percpu_to_op("and", per_cpu__##var, val)
> >>>  #define percpu_or(var, val)	percpu_to_op("or", per_cpu__##var, val)
> >> The final goal is to unify static and dynamic accesses but we 
> >> aren't there yet, so, for the time being, we'll need some interim 
> >> solutions. I would prefer percpu_ptr_add() tho.
> > 
> > Yep, that's the standard naming scheme for new APIs: generic to 
> > specific, left to right.
> > 
> 
> Here is a second version of the patch, with percpu_ptr_xxx convention,
> and more polished form (snmp_mib_free() was forgoten in previous RFC)
> 
> Thank you all
> 
> [PATCH] percpu: convert SNMP mibs to new infra
> 
> Some arches can use percpu infrastructure for safe changes to mibs.
> (percpu_add() is safe against preemption and interrupts), but
> we want the real thing (a single instruction), not an emulation.
> 
> On arches still using an emulation, its better to keep the two views
> per mib and preemption disable/enable
> 
> This shrinks size of mibs by 50%, but also shrinks vmlinux text size
> (minimum IPV4 config)
> 
> $ size vmlinux.old vmlinux.new
>    text    data     bss     dec     hex filename
> 4308458  561092 1728512 6598062  64adae vmlinux.old
> 4303834  561092 1728512 6593438  649b9e vmlinux.new

Wow, that's pretty impressive!

> Signed-off-by: Eric Dumazet <dada1@...mosbay.com>
> ---
>  arch/x86/include/asm/percpu.h |    3 +++

Acked-by: Ingo Molnar <mingo@...e.hu>

As far as x86 goes, feel free to pick it up into any of the 
networking trees, these bits are easily merged and it's probably 
best if the patch stays in a single piece - it looks compact enough 
and if it breaks it's going to break in networking code.

	Ingo
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