Re: [PATCH 01/13] PM: Add wake lock api.

[Uli Luckas <u.luckas@road.de>]

On Friday, 27. February 2009, Pavel Machek wrote:
> On Fri 2009-02-27 15:07:14, Uli Luckas wrote:
> > On Friday, 27. February 2009, Pavel Machek wrote:
> > > On Fri 2009-02-13 17:49:57, Uli Luckas wrote:
> > > > On Friday, 13. February 2009, Matthew Garrett wrote:
> > > > > Userland ABI would then be a single /dev/inhibit_suspend,
> > > > > with the counter being bumped each time an application opens it.
> > > > > It'll automatically be dropped if the application exits without
> > > > > cleaning up.
> > > > >
> > > > > This seems simpler and also avoids any arguments about the naming
> > > > > scheme. What am I missing?
> > > >
> > > > Opening and closing an fd sounds like a lot of overhead. Taking and
> > > > releasing locks if going to be a called with very highg frequency.
> > > > I'd go for an ioctl.
> > >
> > > Ehm?
> > >
> > > And introduce nasty interface, and probably slower too since open() is
> > > time-critical and ioctl() is not? Or do you have benchmarks?
> >
> > No, just specualting as open() needs to do a directory lookup. It also
> > needs to do book keeping. I'd be surprised if open was faster then ioctl.
>
> Unless you measure how much slower it is...
>
OK. Opening /dev/null 100000 times readonly takes 365 ms on my machine. 
Opening it once and then, 100000 times writing 1 byte takes 32 ms.
Why exactly did you think I had to provide numbers???

> > On the otherhand if you consider ioctl nasty, maybe write() is an option?
>
> You want sleepvetos to be automatically unlocked/freed on close and
> process exit/kill, so neither write nor ioctl is the right interface.
An application opens a device node and then writes 1s to take the lock and 0s 
to release it.
Why does that make it impossible to auto-release the lock on close?

Uli


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