RFC: cpuset APIs

Joel Sherrill joel.sherrill at OARcorp.com
Mon Oct 14 14:17:01 UTC 2013

On 10/14/2013 2:22 AM, Sebastian Huber wrote:
> Hello Joel,
> I would provide a super set of the FreeBSD and Linux APIs for RTEMS and use a 
> clean implementation.  In case of conflicts I would use the Linux API.  Its 
> just managing bits.

OK. I will try to post something today or tomorrow.

> On 2013-10-11 23:06, Joel Sherrill wrote:
>> Hi
>> We are finishing up a proposal for pthread affinity APIs. We
>> think we should follow the Linux API but have our own
>> implementation.  I am trying to use the FreeBSD cpu set code
>> with minimal ifdefs, but there are differences which are
>> adding up to the point where I have a problem. Do I put in
>> lots of ifdef's? Or just create our own version using
>> the BSD version as inspiration and code fragements?
>> The first difference is Linux uses cpu_set_t while
>> FreeBSD uses cpuset_t. This can be accounted for with
>> a typedef. A global search and replace or using ifdefs
>> will result in a file with lots of changes. Assume a
>> typedef is OK since it minimizes impact of that.
>> Then you have supporting macros.  The following summarizes
>> the similarities and differences.
>> These macros appear to be the same on Linux and FreeBSD.
>>    void CPU_ZERO(cpu_set_t *set);
>>    void CPU_SET(int cpu, cpu_set_t *set);
>>    void CPU_CLR(int cpu, cpu_set_t *set);
>>    int  CPU_ISSET(int cpu, cpu_set_t *set);
>> For comparing sets, Linux has CPU_EQUAL while BSD has CPU_CMP.
>> The signature is the same so a renaming macro would address this.
>>    int  CPU_EQUAL(cpu_set_t *set1, cpu_set_t *set2);
>> FreeBSD has these extra:
>>    void CPU_FILL(cpu_set_t *set)
>>    bool CPU_EMPTY(cpu_set_t *set) /* is empty? */
>>    bool CPU_SUBSET(cpu_set_t *p,cpu_set_t *c) /* is c a subset of p? */
>>    bool CPU_OVERLAP(cpu_set_t *p,cpu_set_t *c) /* do c and p overlap? */
>> And these differ between FreeBSD and Linux. The Linux API has three
>> parameters and is performs bitwise operations on the two sources
>> and puts the result in destination. FreeBSD has an "|=" or "&="
>> and takes destination and the set to operate with. This is the
>> Linux API. Just drop a parameter to get FreeBSD but that makes
>> them incompatible.
>>    void CPU_AND(cpu_set_t *destset,
>>       cpu_set_t *srcset1, cpu_set_t *srcset2);
>>    void CPU_OR(cpu_set_t *destset,
>>       cpu_set_t *srcset1, cpu_set_t *srcset2);
>>    void CPU_XOR(cpu_set_t *destset,
>>       cpu_set_t *srcset1, cpu_set_t *srcset2);
>> FreeBSD also has NAND.
>> Comments, suggestions, thoughts welcomed.

Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
Support Available                (256) 722-9985

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