[Mesa-dev] [PATCH] gallium/util: don't let children of fork & exec inherit our thread affinity

[Marek Olšák]

On Fri, Sep 14, 2018 at 12:54 PM, Nicholas Miell <nmiell at gmail.com> wrote:
> On 09/12/2018 05:40 PM, Marek Olšák wrote:
>> +static void
>> +util_set_full_cpu_affinity(void)
>> +{
>> +   cpu_set_t cpuset;
>> +
>> +   CPU_ZERO(&cpuset);
>> +   for (unsigned i = 0; i < CPU_SETSIZE; i++)
>> +      CPU_SET(i, &cpuset);
>> +
>> +   pthread_setaffinity_np(pthread_self(), sizeof(cpuset), &cpuset);
>> +}
>>
>>  static void
>> -util_init_cache_number(void)
>> +util_init_thread_pinning(void)
>>  {
>>     /* Get a semi-random number. */
>>     int64_t t = os_time_get_nano();
>>     L3_cache_number = (t ^ (t >> 8) ^ (t >> 16));
>> +
>> +   /* Reset thread affinity for all children of fork and exec to prevent
>> +    * spawned processes and threads from inheriting the current thread's
>> +    * affinity.
>> +    *
>> +    * What happens if a driver is unloaded and the app creates a thread?
>> +    */
>> +   pthread_atfork(NULL, NULL, util_set_full_cpu_affinity);
>>  }
>>
>
> You should probably save and restore the application's affinity mask
> rather than assuming the mask is set to all CPUs.

The affinity mask references a random CCX for each OpenGL context, and
we don't know which thread called fork in the child.

Marek