linux-kernel - Re: [PATCH v5 4/8] smp: Add func to IPI cpus based on parameter func

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Date:	Sun, 8 Jan 2012 18:09:03 +0200
From:	Gilad Ben-Yossef <gilad@...yossef.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Russell King <linux@....linux.org.uk>, linux-mm@...ck.org,
	Pekka Enberg <penberg@...nel.org>,
	Matt Mackall <mpm@...enic.com>,
	Sasha Levin <levinsasha928@...il.com>,
	Rik van Riel <riel@...hat.com>,
	Andi Kleen <andi@...stfloor.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, Avi Kivity <avi@...hat.com>
Subject: Re: [PATCH v5 4/8] smp: Add func to IPI cpus based on parameter func

On Wed, Jan 4, 2012 at 12:34 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Mon,  2 Jan 2012 12:24:15 +0200
> Gilad Ben-Yossef <gilad@...yossef.com> wrote:
>
>> Add the on_each_cpu_required() function that wraps on_each_cpu_mask()
>> and calculates the cpumask of cpus to IPI by calling a function supplied
>> as a parameter in order to determine whether to IPI each specific cpu.
>
> The name is actually "on_each_cpu_cond".

Oopss... I started out with on_each_cpu_required as a name and switched but
missed the description. Thanks for pointing it out.

<SNIP>

>> + * Call a function on each processor for which the supplied function
>> + * cond_func returns a positive value. This may include the local
>> + * processor, optionally waiting for all the required CPUs to finish.
>> + * The function may be called on all online CPUs without running the
>> + * cond_func function in extreme circumstance (memory allocation
>> + * failure condition when CONFIG_CPUMASK_OFFSTACK=y)
>> + * All the limitations specified in smp_call_function_many apply.
>> + */
>> +void on_each_cpu_cond(int (*cond_func) (int cpu, void *info),
>> +                     void (*func)(void *), void *info, bool wait)
>> +{
>> +     cpumask_var_t cpus;
>> +     int cpu;
>> +
>> +     if (likely(zalloc_cpumask_var(&cpus, GFP_ATOMIC))) {
>> +             for_each_online_cpu(cpu)
>> +                     if (cond_func(cpu, info))
>> +                             cpumask_set_cpu(cpu, cpus);
>> +             on_each_cpu_mask(cpus, func, info, wait);
>> +             free_cpumask_var(cpus);
>> +     } else
>> +             on_each_cpu(func, info, wait);
>> +}
>> +EXPORT_SYMBOL(on_each_cpu_cond);
>
> If zalloc_cpumask_var() fails, can we not fall back to
>
>                for_each_online_cpu(cpu)
>                        if (cond_func(cpu, info))
>                                smp_call_function_single(...);
>

Indeed we can and probably should :-)

I'll send out v6 with this and other fixes momentarily.

Thanks,
Gilad

-- 
Gilad Ben-Yossef
Chief Coffee Drinker
gilad@...yossef.com
Israel Cell: +972-52-8260388
US Cell: +1-973-8260388
http://benyossef.com

"Unfortunately, cache misses are an equal opportunity pain provider."
-- Mike Galbraith, LKML
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