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SubjectRe: [PATCH 1/11] Add generic helpers for arch IPI function calls
Jens Axboe wrote:
> On Thu, Apr 24 2008, Russell King wrote:
>
>> On Tue, Apr 22, 2008 at 08:50:17PM +0200, Jens Axboe wrote:
>>
>>> + data->csd.func(data->csd.info);
>>> +
>>> + spin_lock(&data->lock);
>>> + cpu_clear(cpu, data->cpumask);
>>> + WARN_ON(data->refs == 0);
>>> + data->refs--;
>>> + refs = data->refs;
>>>
>> Probably a silly question, but what does data->refs do that
>> cpus_empty(data->cpumask) wouldn't do? (as indeed ARM presently does.)
>>
>
> I guess it can be marginally slower for NR_CPUS > BITS_PER_LONG,
> otherwise there's absolutely no reason to have a seperate ref counter.
>

Jes was concerned about scanning bitmasks on a 4096 CPU Altix. I'm not
sure its all that important, but a refcount check would definitely be
quicker.

J


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