linux-kernel - Re: [linux-pm] Attempted summary of suspend-blockers LKML thread

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Date:	Tue, 03 Aug 2010 11:02:18 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	paulmck@...ux.vnet.ibm.com, peterz@...radead.org,
	swetland@...gle.com, linux-kernel@...r.kernel.org,
	florian@...kler.org, linux-pm@...ts.linux-foundation.org,
	tglx@...utronix.de, alan@...rguk.ukuu.org.uk
Subject: Re: [linux-pm] Attempted summary of suspend-blockers LKML thread

On Mon, 2010-08-02 at 21:18 -0700, Arve Hjønnevåg wrote:
> > o       A power-aware application must be able to efficiently communicate
> >        its needs to the system, so that such communication can be
> >        performed on hot code paths.  Communication via open() and
> >        close() is considered too slow, but communication via ioctl()
> >        is acceptable.
> >
> 
> The problem with using open and close to prevent an allow suspend is
> not that it is too slow but that it interferes with collecting stats.

Please elaborate on this.  I expect the pm-qos stats interface will
collect stats across user open/close because that's how it currently
works.  What's the problem?

> The wakelock code has a sysfs interface that allow you to use a
> open/write/close sequence to block or unblock suspend. There is no
> limit to the amount of kernel memory that a process can consume with
> this interface, so the suspend blocker patchset uses a /dev interface
> with ioctls to block or unblock suspend and it destroys the kernel
> object when the file descriptor is closed.

This is an implementation detail only.  The pm-qos objects are long
lived, so their stats would be too.  I would guess that explicit stat
clearing might be a useful option.

James


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