From: NeilBrown <neilb@suse.de>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: "Linux PM list" <linux-pm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Magnus Damm" <magnus.damm@gmail.com>,
markgross@thegnar.org, "Matthew Garrett" <mjg@redhat.com>,
"Greg KH" <gregkh@linuxfoundation.org>,
"Arve Hjønnevåg" <arve@android.com>,
"John Stultz" <john.stultz@linaro.org>,
"Brian Swetland" <swetland@google.com>,
"Alan Stern" <stern@rowland.harvard.edu>,
"Dmitry Torokhov" <dmitry.torokhov@gmail.com>,
"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
Subject: Re: [RFC][PATCH 5/8] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready
Date: Thu, 26 Apr 2012 14:03:24 +1000 [thread overview]
Message-ID: <20120426140324.0357b1a3@notabene.brown> (raw)
In-Reply-To: <201204222322.44278.rjw@sisk.pl>
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On Sun, 22 Apr 2012 23:22:43 +0200 "Rafael J. Wysocki" <rjw@sisk.pl> wrote:
> From: Arve Hjønnevåg <arve@android.com>
>
> When an epoll_event, that has the EPOLLWAKEUP flag set, is ready, a
> wakeup_source will be active to prevent suspend. This can be used to
> handle wakeup events from a driver that support poll, e.g. input, if
> that driver wakes up the waitqueue passed to epoll before allowing
> suspend.
>
> The current implementation uses an extra wakeup_source when
> ep_scan_ready_list runs. This can cause problems if a single thread
> is polling on wakeup events and frequent non-wakeup events (events
> usually arrive during thread freezing) using the same epoll file.
This is quite neat.
If I understand it correctly, you register file descriptors with epoll_ctl()
on an fd created with epoll_create(), and set the new EPOLLWAKEUP flag.
Then when a regular 'poll' or 'select' on the epoll fd reports that it is
readable you:
- get a wakelock
- use epoll_wait to collect the events
- process the events
- release your wakelock
- go back to poll() or select() on the epoll fd.
Correct? As long as there are ready events with EPOLLWAKEUP set a
wakeup_source is held active and the system won't go to sleep.
My concern with this is about permissions. It appears that any process could
wait of some fd (maybe a pipe they created themselves) with EPOLLWAKEUP, and
then simply never epoll_wait() for the event. Then they would be keeping
the system awake. I don't think that is acceptable.
So there needs to be some way to limit who can effectively block suspend by
using EPOLLWAKEUP.
(This is one of the reasons I like an all-user-space solution. Policy issues
like this can easily be decided in user-space but are clumsy to put into the
kernel).
Also, I'm having trouble understanding the ep->ws wakeup_source.
The epi->ws makes lots of sense and I think I understand it all.
However I don't see why you need a wakeup_source for the 'struct eventpoll'.
Every time that 'poll' decides to call the ->poll fop for the eventpoll, this
wakeup_source will be activated and deactivated which will abort any current
suspend cycle even if there are no events to report.
I suspect it can just go away.
One last item that doesn't really belong here - but it is in context.
This mechanism is elegant because it provides a single implementation that
provides wakeup_source for almost any sort of device. I would like to do the
same thing for interrupts.
Most (maybe all) of the wakeup device on my phone have an interrupt where the
body is run in a thread. When the thread has done it's work the event is
visible to userspace so the EPOLLWAKEUP mechanism is all that is needed to
complete the path to user-space (or for my user-space solution, nothing else
is needed once it is visible to user-space).
So we just need to ensure a clear path from the "top half" interrupt handler
to the threaded handler.
So I imagine attaching a wakeup source to every interrupt for which 'wakeup'
is enabled, activating it when the top-half starts and relaxing it when the
bottom-half completes. With this in place, almost all drivers would get
wakeup_source handling for free.
Does this seem reasonable to you. I'm afraid I don't have code yet, but hope
to find time in a few weeks.
One difficulty with that is that I have noticed a number of drivers that
potentially enable_irq_wake just before suspend and disable_irq_wake
immediately after (e.g. gpio_keys.c). Allocating a wakeup_source on each
enable_irq_wake would be an unfortunate overhead. Maybe we just allocate it
the first time enable_irq_wake is called ....
Thanks,
NeilBrown
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next prev parent reply other threads:[~2012-04-26 4:03 UTC|newest]
Thread overview: 129+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-07 1:00 [RFC][PATCH 0/8] PM: Implement autosleep and "wake locks" Rafael J. Wysocki
2012-02-07 1:01 ` [PATCH 1/8] PM / Sleep: Initialize wakeup source locks in wakeup_source_add() Rafael J. Wysocki
2012-02-07 22:29 ` John Stultz
2012-02-07 22:41 ` Rafael J. Wysocki
2012-02-07 1:03 ` [PATCH 2/8] PM / Sleep: Do not check wakeup too often in try_to_freeze_tasks() Rafael J. Wysocki
2012-02-07 1:03 ` [PATCH 3/8] PM / Sleep: Look for wakeup events in later stages of device suspend Rafael J. Wysocki
2012-02-07 1:04 ` [PATCH 4/8] PM / Sleep: Use wait queue to signal "no wakeup events in progress" Rafael J. Wysocki
2012-02-08 23:10 ` NeilBrown
2012-02-09 0:05 ` Rafael J. Wysocki
2012-02-12 1:27 ` mark gross
2012-02-07 1:05 ` [RFC][PATCH 5/8] PM / Sleep: Change wakeup statistics Rafael J. Wysocki
2012-02-15 6:15 ` Arve Hjønnevåg
2012-02-15 22:37 ` Rafael J. Wysocki
2012-02-17 2:11 ` Arve Hjønnevåg
2012-02-07 1:06 ` [RFC][PATCH 6/8] PM / Sleep: Implement opportunistic sleep Rafael J. Wysocki
2012-02-07 22:49 ` [Update][RFC][PATCH " Rafael J. Wysocki
2012-02-07 1:06 ` [RFC][PATCH 7/8] PM / Sleep: Add "prevent autosleep time" statistics to wakeup sources Rafael J. Wysocki
2012-02-07 1:07 ` [RFC][PATCH 8/8] PM / Sleep: Add user space interface for manipulating " Rafael J. Wysocki
2012-02-07 1:13 ` [RFC][PATCH 0/8] PM: Implement autosleep and "wake locks" Rafael J. Wysocki
2012-02-08 23:57 ` NeilBrown
2012-02-10 0:44 ` Rafael J. Wysocki
2012-02-12 2:05 ` mark gross
2012-02-12 21:32 ` Rafael J. Wysocki
2012-02-14 0:11 ` Arve Hjønnevåg
2012-02-15 15:28 ` mark gross
2012-02-12 1:54 ` mark gross
2012-02-12 1:19 ` mark gross
2012-02-14 2:07 ` Arve Hjønnevåg
2012-02-14 23:22 ` Rafael J. Wysocki
2012-02-15 5:57 ` Arve Hjønnevåg
2012-02-15 23:07 ` Rafael J. Wysocki
2012-02-16 22:22 ` Rafael J. Wysocki
2012-02-17 3:56 ` Arve Hjønnevåg
2012-02-17 23:02 ` [PATCH] PM / Sleep: Add more wakeup source initialization routines Rafael J. Wysocki
2012-02-18 23:50 ` [Update][PATCH] " Rafael J. Wysocki
2012-02-20 23:04 ` [Update 2x][PATCH] " Rafael J. Wysocki
2012-02-17 3:55 ` [RFC][PATCH 0/8] PM: Implement autosleep and "wake locks" Arve Hjønnevåg
2012-02-17 20:57 ` Rafael J. Wysocki
2012-02-21 23:31 ` [RFC][PATCH 0/7] PM: Implement autosleep and "wake locks", take 2 Rafael J. Wysocki
2012-02-21 23:32 ` [RFC][PATCH 1/7] PM / Sleep: Look for wakeup events in later stages of device suspend Rafael J. Wysocki
2012-02-21 23:33 ` [RFC][PATCH 2/7] PM / Sleep: Use wait queue to signal "no wakeup events in progress" Rafael J. Wysocki
2012-02-21 23:34 ` [RFC][PATCH 3/7] PM / Sleep: Change wakeup source statistics to follow Android Rafael J. Wysocki
2012-02-21 23:34 ` [RFC][PATCH 4/7] Input / PM: Add ioctl to block suspend while event queue is not empty Rafael J. Wysocki
2012-02-24 5:16 ` Matt Helsley
2012-02-25 4:25 ` Arve Hjønnevåg
2012-02-25 23:33 ` Rafael J. Wysocki
2012-02-28 0:19 ` Matt Helsley
2012-02-26 20:57 ` Rafael J. Wysocki
2012-02-27 22:18 ` Matt Helsley
2012-02-28 1:17 ` Rafael J. Wysocki
2012-02-28 5:58 ` Arve Hjønnevåg
2012-03-04 22:56 ` Rafael J. Wysocki
2012-03-06 1:04 ` [PATCH 1/2] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready Arve Hjønnevåg
2012-03-06 1:04 ` [PATCH 2/2] PM / Sleep: Add wakeup_source_activate and wakeup_source_deactivate tracepoints Arve Hjønnevåg
2012-02-21 23:35 ` [RFC][PATCH 5/7] PM / Sleep: Implement opportunistic sleep Rafael J. Wysocki
2012-02-22 8:45 ` Srivatsa S. Bhat
2012-02-22 22:10 ` Rafael J. Wysocki
2012-02-23 5:35 ` Srivatsa S. Bhat
2012-02-21 23:36 ` [RFC][PATCH 6/7] PM / Sleep: Add "prevent autosleep time" statistics to wakeup sources Rafael J. Wysocki
2012-02-21 23:37 ` [RFC][PATCH 7/7] PM / Sleep: Add user space interface for manipulating " Rafael J. Wysocki
2012-02-22 4:49 ` [RFC][PATCH 0/7] PM: Implement autosleep and "wake locks", take 2 John Stultz
2012-02-22 8:44 ` Srivatsa S. Bhat
2012-02-22 22:10 ` [RFC][PATCH 0/7] PM: Implement autosleep and "wake locks", take2 Rafael J. Wysocki
2012-02-23 6:25 ` Srivatsa S. Bhat
2012-02-23 21:26 ` Rafael J. Wysocki
2012-02-23 21:32 ` Rafael J. Wysocki
2012-02-24 4:44 ` Srivatsa S. Bhat
2012-02-24 23:21 ` Rafael J. Wysocki
2012-02-25 4:43 ` Arve Hjønnevåg
2012-02-25 20:43 ` Rafael J. Wysocki
2012-02-25 19:20 ` Srivatsa S. Bhat
2012-02-25 21:01 ` Rafael J. Wysocki
2012-02-28 10:24 ` Srivatsa S. Bhat
2012-04-22 21:19 ` [RFC][PATCH 0/8] PM: Implement autosleep and "wake locks", take 3 Rafael J. Wysocki
2012-04-22 21:19 ` [PATCH 1/8] PM / Sleep: Look for wakeup events in later stages of device suspend Rafael J. Wysocki
2012-04-22 21:20 ` [PATCH 2/8] PM / Sleep: Use wait queue to signal "no wakeup events in progress" Rafael J. Wysocki
2012-04-23 4:01 ` mark gross
2012-04-22 21:21 ` [PATCH 3/8] PM / Sleep: Change wakeup source statistics to follow Android Rafael J. Wysocki
2012-04-22 21:21 ` [PATCH 4/8] PM / Sleep: Add wakeup_source_activate and wakeup_source_deactivate tracepoints Rafael J. Wysocki
2012-04-22 21:22 ` [RFC][PATCH 5/8] epoll: Add a flag, EPOLLWAKEUP, to prevent suspend while epoll events are ready Rafael J. Wysocki
2012-04-26 4:03 ` NeilBrown [this message]
2012-04-26 20:40 ` Rafael J. Wysocki
2012-04-27 3:49 ` Arve Hjønnevåg
2012-04-27 21:18 ` Rafael J. Wysocki
2012-04-27 23:26 ` [PATCH] " Arve Hjønnevåg
2012-04-30 1:58 ` [RFC][PATCH 5/8] " NeilBrown
2012-05-01 0:52 ` Arve Hjønnevåg
2012-05-01 2:18 ` NeilBrown
2012-05-01 5:33 ` [PATCH] " Arve Hjønnevåg
2012-05-01 6:28 ` NeilBrown
2012-05-01 13:51 ` Rafael J. Wysocki
2012-07-16 6:38 ` Michael Kerrisk
2012-07-16 11:00 ` Rafael J. Wysocki
2012-07-16 22:04 ` Arve Hjønnevåg
2012-07-17 5:14 ` Michael Kerrisk
2012-07-17 19:22 ` Rafael J. Wysocki
2012-07-17 19:36 ` Greg KH
2012-07-17 19:55 ` Rafael J. Wysocki
2012-07-18 6:41 ` Michael Kerrisk (man-pages)
2012-04-22 21:23 ` [RFC][PATCH 6/8] PM / Sleep: Implement opportunistic sleep Rafael J. Wysocki
2012-04-26 3:05 ` NeilBrown
2012-04-26 21:52 ` Rafael J. Wysocki
2012-04-27 0:39 ` NeilBrown
2012-04-27 21:22 ` Rafael J. Wysocki
2012-05-03 0:23 ` Arve Hjønnevåg
2012-05-03 13:28 ` Rafael J. Wysocki
2012-05-03 21:27 ` Arve Hjønnevåg
2012-05-03 22:20 ` Rafael J. Wysocki
2012-05-03 22:16 ` Arve Hjønnevåg
2012-05-03 22:24 ` Rafael J. Wysocki
2012-04-22 21:24 ` [RFC][PATCH 7/8] PM / Sleep: Add "prevent autosleep time" statistics to wakeup sources Rafael J. Wysocki
2012-04-22 21:24 ` [RFC][PATCH 8/8] PM / Sleep: Add user space interface for manipulating " Rafael J. Wysocki
2012-04-24 1:35 ` John Stultz
2012-04-24 21:27 ` Rafael J. Wysocki
2012-04-26 6:31 ` NeilBrown
2012-04-26 22:04 ` Rafael J. Wysocki
2012-04-27 0:07 ` NeilBrown
2012-04-27 21:15 ` Rafael J. Wysocki
2012-04-27 3:57 ` Arve Hjønnevåg
2012-04-27 21:14 ` Rafael J. Wysocki
2012-04-27 21:17 ` Arve Hjønnevåg
2012-04-27 21:34 ` Rafael J. Wysocki
2012-05-03 19:29 ` [PATCH 0/2]: Kconfig options for wakelocks limit and gc (was: Re: [RFC][PATCH 8/8] PM / Sleep: Add user space ...) Rafael J. Wysocki
2012-05-03 19:30 ` [PATCH 1/2] PM / Sleep: Make the limit of user space wakeup sources configurable Rafael J. Wysocki
2012-05-03 19:34 ` [PATCH 2/2] PM / Sleep: User space wakeup sources garbage collector Kconfig option Rafael J. Wysocki
2012-05-03 22:14 ` [PATCH 0/2]: Kconfig options for wakelocks limit and gc (was: Re: [RFC][PATCH 8/8] PM / Sleep: Add user space ...) Arve Hjønnevåg
2012-05-03 22:20 ` Rafael J. Wysocki
2012-04-23 16:49 ` [RFC][PATCH 0/8] PM: Implement autosleep and "wake locks", take 3 Greg KH
2012-04-23 19:51 ` Rafael J. Wysocki
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