processor namespace

[Holger Macht]

On Wed 23. Aug - 22:29:03, Kay Sievers wrote:
> On Wed, 2006-08-23 at 22:05 +0200, Holger Macht wrote:
> > On Wed 23. Aug - 21:32:15, Kay Sievers wrote:
> > > On Wed, 2006-08-23 at 21:11 +0200, Holger Macht wrote:
> > > > On Wed 23. Aug - 21:51:21, S.Çağlar Onur wrote:
> > > > > Çarşamba 23 Ağustos 2006 20:44 tarihinde, Holger Macht şunları yazmıştı: 
> > > > > > The processor namespace is currently only valid for ACPI. And basically
> > > > > > CPU frequency scaling has nothing to do with ACPI.
> > > > > 
> > > > > I see, but maybe we can add current_frequency and into processor namespace as 
> > > > > it is provided by /proc/cpuinfo [with making 
> > > > > hald/linux/acpi.d:get_processor_model_name more generic and moving into 
> > > > > hald/linux/util.c?]
> > > > > 
> > > > > > Hm, I think simple shell scripts can parse /sys/.../scaling_cur_freq
> > > > > > manually?
> > > > > 
> > > > > Ok, here is what i want to do. Sorry for previous cryptic mails.
> > > > > 
> > > > > I'm trying to write a notification system [1] using libnotify, and for example 
> > > > > inform the user when frequency changed. So what i want to just connect to it 
> > > > > on bus and wait for a signal instead of polling. Or getting free size from 
> > > > > volumes, libhal provides volume.size, volume.block_size but not 
> > > > > volume.free_size. 
> > > > 
> > > > But HAL would have to poll too.
> > > > 
> > > > > 
> > > > > So i just want to know is there any way to get these informations with hal 
> > > > > that currently i dont know, or will be included next releases or i have to 
> > > > > handle these :)
> > > > 
> > > > Currently there is no way to get this information via HAL. And I also
> > > > don't think it makes sence to add it. As long as the kernel is responsible
> > > > to change frequencies, which is the majority of the time, and he doesn't
> > > > export these changes to userspace, there's no possibility other than
> > > > polling.
> > > 
> > > The kernel can wake up a process sleeping in poll() of a sysfs file. If
> > > there is a kernel frequency transition, it would just need to send an
> > > fsnotify() for the file, so processes can wait for a change without
> > > periodically polling.
> > > 
> > > We already do the same for /proc/mounts with HAL, where poll() trows an
> > > error to let the application waiting in poll() to reread the whole file.
> > > 
> > > Sounds like this could also work for the cpufreq representation in
> > > sysfs?
> > 
> > Yes, this should be possible. But frequency transitions are very frequent,
> > so I don't know how relevant performance issues would be...
> 
> Almost nothing, if nobody keeps the file open. But sure the watching
> process will be woken up on every change, but it would probably still
> better than dumb periodical polling.

Yes, of course better than polling .

> 
> Btw: I'm almost sure, that such a feature is not very useful outside of
> a weird hacker desktop. I think that displaying the current processor
> frequency in the taskbar or wherever, is a pretty useless thing for the
> average user. :)

Agreed, see my other mail ;-)


Regards,
	Holger