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

[Marek Olšák]

On Thu, Sep 13, 2018 at 11:48 AM, Michel Dänzer <michel at daenzer.net> wrote:
> On 2018-09-13 2:40 a.m., Marek Olšák wrote:
>> From: Marek Olšák <marek.olsak at amd.com>
>>
>> [...]
>>
>>  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
>
> I don't think exec (which doesn't spawn a child, it replaces the current
> process "image" with a new one) has anything to do with this.
>
>
>> +    * spawned processes and threads from inheriting the current thread's
>> +    * affinity.
>
> As the name implies, pthread_atfork only affects child processes spawned
> with fork(), not new threads. As such, I'm afraid this won't help at
> least for blender, which AFAICT doesn't call fork, it only spawns threads.

All created threads and processes are just some variants of fork. They
all inherit affinity of the parent process/thread.

This patch is enough to stop inheriting thread affinity from X and
gnome-shell to GL apps, to gcc run within an X terminal, etc.
Everything within X inherits the thread affinity of X or gnome-shell,
including gcc.

Marek