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

[Petri Latvala]

On Thu, Mar 18, 2021 at 02:48:36PM +0100, Zbigniew Kempczyński wrote:
> 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?

Not sure if they need to but maintaining their pid/tid tracking might
be useful for other stuff. I might have a big patch series coming that
could use it...

Either way it's a discrepancy, not a real concern at this point.


-- 
Petri Latvala