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

From: James Bottomley
Date: Tue Aug 03 2010 - 12:02:31 EST

On Mon, 2010-08-02 at 21:18 -0700, Arve HjÃnnevÃg 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.


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