linux-kernel - Re: [PATCH] generic-ipi: make struct call_function

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Message-ID: <20090729070801.GH4148@kernel.dk>
Date:	Wed, 29 Jul 2009 09:08:01 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Nick Piggin <nickpiggin@...oo.com.au>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] generic-ipi: make struct call_function_data lockless

On Fri, Jul 24 2009, Xiao Guangrong wrote:
> This patch can remove spinlock from struct call_function_data, the 
> reasons are below:
> 
> 1: add a new interface for cpumask named cpumask_test_and_clear_cpu(),
>    it can atomically test and clear specific cpu, we can use it instead
>    of cpumask_test_cpu() and cpumask_clear_cpu() and no need data->lock
>    to protect those in generic_smp_call_function_interrupt().
> 
> 2: in smp_call_function_many(), after csd_lock() return, the current's
>    cfd_data is deleted from call_function list, so it not have race
>    between other cpus, then cfs_data is only used in
>    smp_call_function_many() that must disable preemption and not from
>    a hardware interrupthandler or from a bottom half handler to call,
>    only the correspond cpu can use it, so it not have race in current
>    cpu, no need cfs_data->lock to protect it.
> 
> 3: after 1 and 2, cfs_data->lock is only use to protect cfs_data->refs in
>    generic_smp_call_function_interrupt(), so we can define cfs_data->refs
>    to atomic_t, and no need cfs_data->lock any more.

Very nice, looks good to me! Tested on x86-64 and sparc64 here.
Andrew, shall I include it, or shall we just let it funnel through
your patch stream?

Acked-by: Jens Axboe <jens.axboe@...cle.com>

-- 
Jens Axboe

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