Re: [RFC] Cpu-hotplug: Using the Process Freezer (try2)



On Mon, Apr 02, 2007 at 08:16:12AM +0200, Ingo Molnar wrote:

i'm wondering about how TASK_UNINTERRUPTIBLE tasks are handled by the
freezer: are they assumed frozen immediately, or do we wait until they
notice their PF_FREEZING and go into try_to_freeze()? I'd expect
TASK_UNINTERRUPTIBLE to be the largest source of latency. (and hence be
the primary source for freezing 'failures')

Ok, we might be in some luck. I panic()ed on freezer fail and checked
the stacktrace of the unfrozen tasks. The stacktrace of each one looks
like:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
PID: 7697 TASK: cc354a70 CPU: 7 COMMAND: "make"
#0 [cc37fe50] schedule at c0431752
#1 [cc37fec4] wait_for_completion at c04318d0
#2 [cc37ff24] do_fork at c01249a6
#3 [cc37ff94] sys_vfork at c0103c1f
#4 [cc37ffb4] system_call at c0104d8d
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Rafael had sent out a patch to fix the vfork race, which can be found at
http://lkml.org/lkml/2007/3/1/212

However, the hunk

@@ -1393,7 +1394,9 @@ long do_fork(unsigned long clone_flags,
tracehook_report_clone_complete(clone_flags, nr, p);

if (clone_flags & CLONE_VFORK) {
+ freezer_do_not_count();
wait_for_completion(&vfork);
+ freezer_count();
tracehook_report_vfork_done(p, nr);
}
} else {

Seems to be missing in the latest -mm's.

Rafael / Andrew,
Any reasons for leaving this hunk out?

I will rerun my tests with this hunk applied and report back.


Ingo

Thanks and Regards
gautham.
--
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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