Messages in this thread | | | Date | Wed, 28 Mar 2012 13:20:33 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 21/32] nohz/cpuset: Flush cputime on threads in nohz cpusets when waiting leader |
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On Tue, Mar 27, 2012 at 04:23:14PM +0200, Gilad Ben-Yossef wrote: > On Tue, Mar 27, 2012 at 4:10 PM, Gilad Ben-Yossef <gilad@benyossef.com> wrote: > > On Wed, Mar 21, 2012 at 3:58 PM, Frederic Weisbecker <fweisbec@gmail.com> wrote: > >> When we wait for a zombie task, flush the cputimes on nohz cpusets > >> in case we are waiting for a group leader that has threads running > >> in nohz CPUs. This way thread_group_times() doesn't report stale > >> values. > >> > >> <doubts> > >> If I understood well the code, by the time we call that thread_group_times(), > >> we may have childs that are still running, so this is necessary. > >> But I need to check deeper. > >> </doubts> > >> > > ... > >> > >> diff --git a/kernel/exit.c b/kernel/exit.c > >> index 4b4042f..c194662 100644 > >> --- a/kernel/exit.c > >> +++ b/kernel/exit.c > >> @@ -52,6 +52,7 @@ > >> #include <linux/hw_breakpoint.h> > >> #include <linux/oom.h> > >> #include <linux/writeback.h> > >> +#include <linux/cpuset.h> > >> > >> #include <asm/uaccess.h> > >> #include <asm/unistd.h> > >> @@ -1712,6 +1713,13 @@ repeat: > >> (!wo->wo_pid || hlist_empty(&wo->wo_pid->tasks[wo->wo_type]))) > >> goto notask; > >> > >> + /* > >> + * For cputime in sub-threads before adding them. > >> + * Must be called outside tasklist_lock lock because write lock > >> + * can be acquired under irqs disabled. > >> + */ > >> + cpuset_nohz_flush_cputimes(); > >> + > >> set_current_state(TASK_INTERRUPTIBLE); > >> read_lock(&tasklist_lock); > >> tsk = current; > >> -- > >> 1.7.5.4 > >> > > > > I believe this patch is not needed because after this point we call > > do_wait_thread /ptrace_do_wait, which both call wait_consider_task, > > which calls wait_task_stopped/zombie/continued, which all eventually > > calls getrusage, which calls k_getrusage where you added a call to > > cpuset_noz_flush_cputimes() in another patch :-) > > > > OK, I now see that wait_task_zombie actually calls > thread_group_times() directly, unlike other wait_task_* > what I wrote above is not needed. > > It does result in more then one IPI for each isolated core (something > like 3 really) for the other cases though: > one from this patch and the rest from the one in k_getrusage calls.
Yeah I realize we may be calling getrusage() from each of the wait_*() things if the user request the rusage. That plus the IPI done in this patch this is too much.
> > I wonder what would be a better way to do it. In theory we can send > the IPI only to nohz cpuset cores that actually > run tasks form the thread group. Finding which is not trivial though...
I also realize that we only call wait_task_zombie() on group leaders if they don't have any subthread left (see delay_group_leader() test). But then we call thread_group_times() to get the time of all threads in the group from wait_task_zombie().
Now I'm confused.
> > Gilad > > > Gilad > > > > -- > > Gilad Ben-Yossef > > Chief Coffee Drinker > > gilad@benyossef.com > > Israel Cell: +972-52-8260388 > > US Cell: +1-973-8260388 > > http://benyossef.com > > > > "If you take a class in large-scale robotics, can you end up in a > > situation where the homework eats your dog?" > > -- Jean-Baptiste Queru > > > > -- > Gilad Ben-Yossef > Chief Coffee Drinker > gilad@benyossef.com > Israel Cell: +972-52-8260388 > US Cell: +1-973-8260388 > http://benyossef.com > > "If you take a class in large-scale robotics, can you end up in a > situation where the homework eats your dog?" > -- Jean-Baptiste Queru -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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