Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964852AbZGQPvj (ORCPT ); Fri, 17 Jul 2009 11:51:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S964835AbZGQPvj (ORCPT ); Fri, 17 Jul 2009 11:51:39 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:60273 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964830AbZGQPvi (ORCPT ); Fri, 17 Jul 2009 11:51:38 -0400 Date: Fri, 17 Jul 2009 08:51:17 -0700 From: Matt Helsley To: Thomas Gleixner Cc: LKML , Andrew Morton , Rafael Wysocki , Ingo Molnar , Peter Zijlstra , Nathan Lynch , Nigel Cunningham , stable@kernel.org, containers@lists.linux-foundation.org, linux-pm@lists.linux-foundation.org, Matt Helsley Subject: Re: [patch 2/2] sched: fix nr_uninterruptible accounting of frozen tasks really Message-ID: <20090717155116.GB5878@count0.beaverton.ibm.com> References: <20090717121545.489258927@linutronix.de> <20090717122103.225652146@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090717122103.225652146@linutronix.de> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5221 Lines: 135 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 > Cc: Nathan Lynch > Cc: Andrew Morton > Cc: Nigel Cunningham > Cc: > Cc: containers@lists.linux-foundation.org > Cc: linux-pm@lists.linux-foundation.org > Cc: Matt Helsley > > --- > 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 -- 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/