[igt-dev] [PATCH i-g-t v26 04/35] lib/igt_core: Track child process pid and tid

[Zbigniew Kempczyński]

On Thu, Mar 18, 2021 at 11:07:46AM +0200, Petri Latvala wrote:
> On Wed, Mar 17, 2021 at 03:45:39PM +0100, Zbigniew Kempczyński wrote:
> > Introduce variables which can decrease number of getpid()/gettid()
> > calls, especially for allocator which must be aware of method
> > acquiring addresses.
> > 
> > When child is spawned using igt_fork() we can control its initialization
> > and prepare child_pid implicitly. Tracking child_tid requires our
> > intervention in the code and do something like this:
> > 
> > if (child_tid == -1)
> > 	child_tid = gettid()
> > 
> > Variable was created for using in TLS so each thread is created
> > with variable set to -1. This will give each thread it's own "copy"
> > and there's no risk to use other thread tid. For each forked child
> > we reassign -1 to child_tid to avoid using already set variable.
> > 
> > Signed-off-by: Zbigniew Kempczyński <zbigniew.kempczynski at intel.com>
> > Cc: Dominik Grzegorzek <dominik.grzegorzek at intel.com>
> > Cc: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Petri Latvala <petri.latvala at intel.com>
> > Acked-by: Arjun Melkaveri <arjun.melkaveri at intel.com>
> > ---
> >  lib/igt_core.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/lib/igt_core.c b/lib/igt_core.c
> > index f9dfaa0dd..2b4182f16 100644
> > --- a/lib/igt_core.c
> > +++ b/lib/igt_core.c
> > @@ -306,6 +306,10 @@ int num_test_children;
> >  int test_children_sz;
> >  bool test_child;
> >  
> > +/* For allocator purposes */
> > +pid_t child_pid  = -1;
> > +__thread pid_t child_tid  = -1;
> > +
> >  enum {
> >  	/*
> >  	 * Let the first values be used by individual tests so options don't
> > @@ -2302,6 +2306,8 @@ bool __igt_fork(void)
> >  	case 0:
> >  		test_child = true;
> >  		pthread_mutex_init(&print_mutex, NULL);
> > +		child_pid = getpid();
> > +		child_tid = -1;
> >  		exit_handler_count = 0;
> >  		reset_helper_process_list();
> >  		oom_adjust_for_doom();
> 
> 
> What about igt_fork_helper?
> 
> -- 
> Petri Latvala

I'm not sure I've understand your concerns. Do you mean 
that helpers spawned by igt_fork_helper() also should 
be allowed to use allocator infrastructure?

--
Zbigniew