linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 29 May 2010 14:55:24 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Florian Mickler <florian@...kler.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Peter Zijlstra <peterz@...radead.org>,
	Paul@...p1.linux-foundation.org,
	LKML <linux-kernel@...r.kernel.org>, felipe.balbi@...ia.com,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

2010/5/29 Rafael J. Wysocki <rjw@...k.pl>:
> On Saturday 29 May 2010, Arve Hjønnevåg wrote:
>> 2010/5/28 Rafael J. Wysocki <rjw@...k.pl>:
>> > On Friday 28 May 2010, Arve Hjønnevåg wrote:
>> >> On Fri, May 28, 2010 at 1:44 AM, Florian Mickler <florian@...kler.org> wrote:
>> >> > On Thu, 27 May 2010 20:05:39 +0200 (CEST)
>> >> > Thomas Gleixner <tglx@...utronix.de> wrote:
>> > ...
>> >> > To integrate this with the current way of doing things, i gathered it
>> >> > needs to be implemented as an idle-state that does the suspend()-call?
>> >> >
>> >>
>> >> I think it is better no not confuse this with idle. Since initiating
>> >> suspend will cause the system to become not-idle, I don't think is is
>> >> beneficial to initiate suspend from idle.
>> >
>> > It is, if the following two conditions hold simultaneously:
>> >
>> > (a) Doing full system suspend is ultimately going to bring you more energy
>> >    savings than the (presumably lowest) idle state you're currently in.
>> >
>> > (b) You anticipate that the system will stay idle for a considerably long time
>> >    such that it's worth suspending.
>> >
>>
>> I still don't think this matters. If you are waiting for in interrupt
>> that cannot wake you up from suspend, then idle is not an indicator
>> that it is safe to enter suspend. I also don't think you can avoid any
>> user-space suspend blockers by delaying suspend until the system goes
>> idle since any page fault could cause it to go idle. Therefore I don't
>> see a benefit in delaying suspend until idle when the last suspend
>> blocker is released (it would only mask possible race conditions).
>
> I wasn't referring to suspend blockers, but to the idea of initiating full
> system suspend from idle, which I still think makes sense.  If you are
> waiting for an interrupt that cannot wake you from suspend, then
> _obviously_ suspend should not be started.  However, if you're not waiting for
> such an interrupt and the (a) and (b) above hold, it makes sense to start
> suspend from idle.
>

What about timers? When you suspend timers stop (otherwise it is just
a deep-idle mode), and this could cause problems. Some drivers rely on
timers if the hardware does not have a completion interrupt. It is not
uncommon to see send command x then wait 200ms in a some hardware
specs.

-- 
Arve Hjønnevåg
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/