From: Srivatsa Vaddagiri <vatsa@in.ibm.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: Gautham R Shenoy <ego@in.ibm.com>,
akpm@linux-foundation.org, paulmck@us.ibm.com,
torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
Oleg Nesterov <oleg@tv-sign.ru>,
"Rafael J. Wysocki" <rjw@sisk.pl>,
dipankar@in.ibm.com, dino@in.ibm.com,
masami.hiramatsu.pt@hitachi.com
Subject: Re: [RFC] Cpu-hotplug: Using the Process Freezer (try2)
Date: Tue, 3 Apr 2007 18:26:19 +0530 [thread overview]
Message-ID: <20070403125619.GA32444@in.ibm.com> (raw)
In-Reply-To: <20070402185607.GA2081@elte.hu>
On Mon, Apr 02, 2007 at 08:56:07PM +0200, Ingo Molnar wrote:
> ok. But the only real problem would be for_each_online_cpu() loops that
> might sleep, correct?
I would shy from saying that "that's the only problem". It could also be
for_each_cpu_mask(some_mask)
do_something_which_sleeps();
where some_mask is suppsoed to represent a subset of online cpus.
For ex: policy->cpus is a mask maintained by cpufreq, which it iterates thr'
whenever changing cpu frequency. The cpus in that mask are supposed to be
a subset of online cpus (with CPU_ONLINE/DEAD handlers in cpufreq.c adjusting
the mask upon hotplug).
We could adopt a similar trick (get/put_each_cpu_mask) that you describe
below in those extended cases as well.
> the 10% loops that _can_ schedule would trigger the __might_sleep()
> atomicity test in schedule()), and those would have to be converted a
> bit more cleverly, on a case by case basis.
The real question is how do we convert over those sleeping
for_each_cpu_mask users (for ex: flush_workqueue) such that they don't
block freezer/hotplug for long periods?
One option is to probably rewrite them to understand that
online[or a derived]_map could have changed everytime they come out of a
(un)interruptible sleep and deal with arising races appropriately. That
would mean a bit of maintenance headache unfortunately (I was hoping
freezer will lead to zero maintenance headache :)
Besides, how problematic is this in practise (that threads sleep for
extended durations in TASK_INTERRUPTIBLE state breaking
freezer/suspend/hotplug)?
Should we ignore this for the timebeing and take up later as and when
users report problems?
--
Regards,
vatsa
next prev parent reply other threads:[~2007-04-03 12:48 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-02 5:34 [RFC] Cpu-hotplug: Using the Process Freezer (try2) Gautham R Shenoy
2007-04-02 5:37 ` [PATCH 1/8] Enhance process freezer interface for usage beyond software suspend Gautham R Shenoy
2007-04-02 13:56 ` Pavel Machek
2007-04-02 20:48 ` Rafael J. Wysocki
2007-04-02 20:51 ` Pavel Machek
2007-04-06 14:34 ` Rafael J. Wysocki
2007-04-06 22:20 ` Nigel Cunningham
2007-04-07 9:33 ` Rafael J. Wysocki
2007-04-07 9:47 ` Nigel Cunningham
2007-04-09 3:04 ` Gautham R Shenoy
2007-04-03 7:59 ` Gautham R Shenoy
2007-04-05 9:46 ` Oleg Nesterov
2007-04-05 10:59 ` Gautham R Shenoy
2007-04-05 11:30 ` Oleg Nesterov
2007-04-02 5:37 ` [PATCH 2/8] Make process freezer reentrant Gautham R Shenoy
2007-04-05 9:53 ` Oleg Nesterov
2007-04-05 10:19 ` Gautham R Shenoy
2007-04-02 5:38 ` [PATCH 3/8] Use process freezer for cpu-hotplug Gautham R Shenoy
2007-04-05 10:53 ` Oleg Nesterov
2007-04-05 12:14 ` Gautham R Shenoy
2007-04-05 13:34 ` Oleg Nesterov
2007-04-06 17:27 ` Nathan Lynch
2007-04-06 17:34 ` Ingo Molnar
2007-04-06 17:47 ` Nathan Lynch
2007-04-06 22:22 ` Nigel Cunningham
2007-04-14 18:48 ` Pavel Machek
2007-04-02 5:39 ` [PATCH 4/8] Rip out lock_cpu_hotplug() Gautham R Shenoy
2007-04-02 5:40 ` [PATCH 5/8] __cpu_up: use singlethreaded workqueue Gautham R Shenoy
2007-04-05 12:08 ` Oleg Nesterov
2007-04-02 5:41 ` [PATCH 6/8] Make non-singlethreaded workqueues freezeable by default Gautham R Shenoy
2007-04-05 11:57 ` Oleg Nesterov
2007-04-05 20:06 ` Andrew Morton
2007-04-02 5:42 ` [PATCH 7/8] Clean up workqueue.c with respect to the freezer based cpu-hotplug Gautham R Shenoy
2007-04-03 11:47 ` Oleg Nesterov
2007-04-03 13:59 ` Srivatsa Vaddagiri
2007-04-03 15:03 ` Oleg Nesterov
2007-04-03 17:18 ` Srivatsa Vaddagiri
2007-04-04 15:28 ` Oleg Nesterov
2007-04-04 17:49 ` Srivatsa Vaddagiri
2007-04-05 12:20 ` Oleg Nesterov
2007-04-12 2:22 ` Srivatsa Vaddagiri
2007-04-12 10:01 ` Gautham R Shenoy
2007-04-12 16:00 ` Oleg Nesterov
2007-04-13 9:46 ` Gautham R Shenoy
2007-04-02 5:42 ` [PATCH 8/8] Make kernel threads freezeable for cpu-hotplug Gautham R Shenoy
2007-04-02 6:16 ` [RFC] Cpu-hotplug: Using the Process Freezer (try2) Ingo Molnar
2007-04-02 9:28 ` Srivatsa Vaddagiri
2007-04-02 11:18 ` Ingo Molnar
2007-04-02 12:42 ` Srivatsa Vaddagiri
2007-04-02 14:16 ` Gautham R Shenoy
2007-04-02 18:56 ` Ingo Molnar
2007-04-03 12:56 ` Srivatsa Vaddagiri [this message]
2007-04-03 14:15 ` Gautham R Shenoy
2007-04-03 19:25 ` Rafael J. Wysocki
2007-04-04 3:15 ` Srivatsa Vaddagiri
2007-04-04 10:04 ` Ingo Molnar
2007-04-04 10:41 ` Gautham R Shenoy
2007-04-04 11:49 ` Ingo Molnar
2007-04-04 12:24 ` Gautham R Shenoy
2007-04-02 11:19 ` Gautham R Shenoy
2007-04-02 11:27 ` Ingo Molnar
2007-04-02 22:12 ` Rafael J. Wysocki
2007-04-02 13:22 ` Pavel Machek
2007-04-03 12:01 ` Gautham R Shenoy
2007-04-03 19:34 ` Rafael J. Wysocki
2007-04-03 20:24 ` Andrew Morton
2007-04-04 10:06 ` utrace merge Ingo Molnar
2007-04-04 10:36 ` Christoph Hellwig
2007-04-04 18:41 ` Andrew Morton
2007-04-03 14:01 ` [RFC] Cpu-hotplug: Using the Process Freezer (try2) Gautham R Shenoy
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