Messages in this thread Patch in this message | | | Date | Fri, 17 Jul 2009 08:51:17 -0700 | From | Matt Helsley <> | Subject | Re: [patch 2/2] sched: fix nr_uninterruptible accounting of frozen tasks really |
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On Fri, Jul 17, 2009 at 12:25:01PM -0000, Thomas Gleixner wrote: > commit e3c8ca8336 (sched: do not count frozen tasks toward load) broke > the nr_uninterruptible accounting on freeze/thaw. On freeze the task > is excluded from accounting with a check for (task->flags & > PF_FROZEN), but that flag is cleared before the task is thawed. So > while we prevent that the freezing task with state > TASK_UNINTERRUPTIBLE is accounted to nr_uninterruptible we decrement > nr_uninterruptible on thaw. > > Use a separate flag which is handled by the freezing task itself. Set > it before calling the scheduler with TASK_UNINTERRUPTIBLE state and > clear it after we return from frozen state.
I'm sorry, it's not clear to me based on the description what problem is being fixed. As far as I can see PF_FROZEN is almost exactly the same as PF_FREEZING. When a task is being frozen TIF_FREEZE is set. Then the task enters the refrigerator, sets PF_FROZEN, and schedule()s until PF_FROZEN is no longer set. The original code with extra comments:
static inline void frozen_process(void) { if (!unlikely(current->flags & PF_NOFREEZE)) { current->flags |= PF_FROZEN; wmb(); } clear_freeze_flag(current); }
/* Refrigerator is place where frozen processes are stored :-). */ void refrigerator(void) { /* Hmm, should we be allowed to suspend when there are realtime processes around? */ long save;
task_lock(current); if (freezing(current)) { /* prevent accounting of that task to load */ frozen_process(); /* <-- sets PF_FROZEN */ task_unlock(current); } else { task_unlock(current); return; } save = current->state; pr_debug("%s entered refrigerator\n", current->comm);
spin_lock_irq(¤t->sighand->siglock); recalc_sigpending(); /* We sent fake signal, clean it up */ spin_unlock_irq(¤t->sighand->siglock);
/* you set PF_FREEZING here */ for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); if (!frozen(current)) /* <-- checks PF_FROZEN */ break; schedule(); } /* you clear PF_FREEZING here */ pr_debug("%s left refrigerator\n", current->comm); __set_current_state(save); }
> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Cc: Nathan Lynch <ntl@pobox.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Nigel Cunningham <nigel@tuxonice.net> > Cc: <stable@kernel.org> > Cc: containers@lists.linux-foundation.org > Cc: linux-pm@lists.linux-foundation.org > Cc: Matt Helsley <matthltc@us.ibm.com> > > --- > include/linux/sched.h | 3 ++- > kernel/freezer.c | 7 +++++++ > 2 files changed, 9 insertions(+), 1 deletion(-) > > Index: linux-2.6/include/linux/sched.h > =================================================================== > --- linux-2.6.orig/include/linux/sched.h > +++ linux-2.6/include/linux/sched.h > @@ -209,7 +209,7 @@ extern unsigned long long time_sync_thre > ((task->state & (__TASK_STOPPED | __TASK_TRACED)) != 0) > #define task_contributes_to_load(task) \ > ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \ > - (task->flags & PF_FROZEN) == 0) > + (task->flags & PF_FREEZING) == 0) > > #define __set_task_state(tsk, state_value) \ > do { (tsk)->state = (state_value); } while (0) > @@ -1680,6 +1680,7 @@ extern cputime_t task_gtime(struct task_ > #define PF_MEMALLOC 0x00000800 /* Allocating memory */ > #define PF_FLUSHER 0x00001000 /* responsible for disk writeback */ > #define PF_USED_MATH 0x00002000 /* if unset the fpu must be initialized before use */ > +#define PF_FREEZING 0x00004000 /* freeze in progress. do not account to load */ > #define PF_NOFREEZE 0x00008000 /* this thread should not be frozen */ > #define PF_FROZEN 0x00010000 /* frozen for system suspend */ > #define PF_FSTRANS 0x00020000 /* inside a filesystem transaction */ > Index: linux-2.6/kernel/freezer.c > =================================================================== > --- linux-2.6.orig/kernel/freezer.c > +++ linux-2.6/kernel/freezer.c > @@ -44,12 +44,19 @@ void refrigerator(void) > recalc_sigpending(); /* We sent fake signal, clean it up */ > spin_unlock_irq(¤t->sighand->siglock); > > + /* prevent accounting of that task to load */ > + current->flags |= PF_FREEZING; > + > for (;;) { > set_current_state(TASK_UNINTERRUPTIBLE); > if (!frozen(current)) > break; > schedule(); > } > + > + /* Remove the accounting blocker */ > + current->flags &= ~PF_FREEZING; > +
Hence PF_FREEZING covers slightly less time than PF_FROZEN but otherwise does not change the way nr_uninterruptible is incremented or decremented (in (de)activate_task()).
So it's not clear to me how adding PF_FREEZING fixes anything. Am I missing something?
Cheers, -Matt Helsley
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