linux-kernel - Re: [PATCH 01/10] cpumask: Introduce cpumask_any_online

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Message-ID: <alpine.DEB.2.10.1506150945540.3447@vshiva-Udesk>
Date:	Mon, 15 Jun 2015 09:48:40 -0700 (PDT)
From:	Vikas Shivappa <vikas.shivappa@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Vikas Shivappa <vikas.shivappa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, vikas.shivappa@...el.com,
	x86@...nel.org, hpa@...or.com, tglx@...utronix.de,
	mingo@...nel.org, matt.fleming@...el.com, will.auld@...el.com,
	linux-rdt@...ists.intel.com
Subject: Re: [PATCH 01/10] cpumask: Introduce cpumask_any_online_but



On Mon, 15 Jun 2015, Peter Zijlstra wrote:

> On Fri, Jun 12, 2015 at 11:17:08AM -0700, Vikas Shivappa wrote:
>> There is currently no cpumask helper function to pick a "random" cpu
>> from a mask which is also online.
>>
>> cpumask_any_online_but() does that which is similar to cpumask_any_but()
>> but also returns a cpu that is online.
>>
>> Signed-off-by: Vikas Shivappa <vikas.shivappa@...ux.intel.com>
>> ---
>>  include/linux/cpumask.h | 18 ++++++++++++++++++
>>  1 file changed, 18 insertions(+)
>>
>> diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
>> index 27e285b..f2d7e8a 100644
>> --- a/include/linux/cpumask.h
>> +++ b/include/linux/cpumask.h
>> @@ -548,6 +548,24 @@ static inline void cpumask_copy(struct cpumask *dstp,
>>  #define cpumask_of(cpu) (get_cpu_mask(cpu))
>>
>>  /**
>> + * cpumask_any_online_but - return a "random"  and online cpu in a cpumask,
>> + * but not this one
>> + * @mask: the input mask to search
>> + * @cpu: the cpu to ignore
>> + *
>> + * Returns >= nr_cpu_ids if no cpus set.
>> +*/
>> +static inline unsigned int cpumask_any_online_but(const struct cpumask *mask,
>> +					   unsigned int cpu)
>> +{
>> +	cpumask_t tmp;
>
> No, you cannot put a cpumask_t on stack like that. Those things can be
> massive.

ok , Will fix.

>
>> +
>> +	cpumask_and(&tmp, cpu_online_mask, mask);
>> +	cpumask_clear_cpu(cpu, &tmp);
>> +	return cpumask_any(&tmp);
>> +}
>
> You had a good example in cpumask_any_but() copy that.

I saw the cpumask_any_but but wanted to avoid the 
for loop in the cpumask_any_but , but now i see why from your previous comment. 
Without the cpumask_t I will have to use the cpumask_any_but .. the two were 
related.

Thanks,
Vikas

>
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