Project Home
Project Home		 Documents
Documents		 Wiki
Wiki		 Discussion Forums
Discussions		 Project Information
Project Info
QNX Operating System/Discussion/OSTech/QNX cpu frequency scaling ?/List of Posts
Forum Topic - QNX cpu frequency scaling ?: (7 Items)
   
Update
Prem Mallappa(deleted)
01/15/2008 11:00 PM
post4341
QNX cpu frequency scaling ?   
Hi,
I am interested to know if QNX supports CPU frequency scaling dynamically.

/Prem
Brian Stecher
01/16/2008 8:56 AM
post4348
Re: QNX cpu frequency scaling ?   
On Tue, Jan 15, 2008 at 11:00:05PM -0500, Prem Mallappa wrote:
> I am interested to know if QNX supports CPU frequency scaling dynamically.

There's nothing specific in the OS to do it. On some hardware, you just
have to enable it (in the BSP) and everything else is taken care of
automatically. On others you might have to write a manager process that
shifted it up and down.

	Brian

-- 
Brian Stecher (bstecher@qnx.com)        QNX Software Systems
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
Attilla Danko(deleted)
01/16/2008 10:42 AM
post4356
Re: QNX cpu frequency scaling ?   
For those systems that do support frequency scaling, how does it affect
clockcycles()?

Brian Stecher wrote:
> On Tue, Jan 15, 2008 at 11:00:05PM -0500, Prem Mallappa wrote:
>  > I am interested to know if QNX supports CPU frequency scaling 
> dynamically.
> 
> There's nothing specific in the OS to do it. On some hardware, you just
> have to enable it (in the BSP) and everything else is taken care of
> automatically. On others you might have to write a manager process that
> shifted it up and down.
> 
>         Brian
Brian Stecher
01/16/2008 12:05 PM
post4361
Re: QNX cpu frequency scaling ?   
On Wed, Jan 16, 2008 at 10:42:06AM -0500, Attilla Danko wrote:
> For those systems that do support frequency scaling, how does it affect
> clockcycles()?

Tell me the system and I'll tell you how it affects ClockCycles() :-).

Seriously, on some hardware the rate that ClockCycles() increments will
be affected as well when the CPU clock slows down (which can cause some 
grief) and on some it won't. On others there'll be a bit somewhere that
controls what happens.

	Brian

-- 
Brian Stecher (bstecher@qnx.com)        QNX Software Systems
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
Attilla Danko(deleted)
01/16/2008 12:12 PM
post4362
Re: QNX cpu frequency scaling ?   
Hmm. I was thinking if I needed to document that for APS.

I've documented that aps assumes that clockcycles() increases monotonically
at
a constant rate and that that rate is proportional to work done. So I'm
covered
from a "legalese" point of view.

But it would probably good for the docs to list the boards/BSPs that break
that
assumption.

Would you know who I should ask?

-ad


Brian Stecher wrote:
> On Wed, Jan 16, 2008 at 10:42:06AM -0500, Attilla Danko wrote:
>  > For those systems that do support frequency scaling, how does it affect
>  > clockcycles()?
> 
> Tell me the system and I'll tell you how it affects ClockCycles() :-).
> 
> Seriously, on some hardware the rate that ClockCycles() increments will
> be affected as well when the CPU clock slows down (which can cause some
> grief) and on some it won't. On others there'll be a bit somewhere that
> controls what happens.
> 
>         Brian
> 
> -- 
> Brian Stecher (bstecher@qnx.com)        QNX Software Systems
> phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
>        +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
> 
> _______________________________________________
> OSTech
> http://community.qnx.com/sf/go/post4361
>
Brian Stecher
01/16/2008 3:32 PM
post4367
Re: QNX cpu frequency scaling ?   
On Wed, Jan 16, 2008 at 12:12:14PM -0500, Attilla Danko wrote:
> But it would probably good for the docs to list the boards/BSPs that break
> that
> assumption.
> 
> Would you know who I should ask?

I don't think anyone "knows" - it's a matter of looking at the CPU's on each
of the board, then reading the chip doc to see if it does frequency 
scaling and figuring out if the ClockCycles() timer is affected by it and
if we enable the frequency scaling feature in the BSP.

	Brian

-- 
Brian Stecher (bstecher@qnx.com)        QNX Software Systems
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr.
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8
Colin Burgess(deleted)
01/16/2008 3:36 PM
post4369
Re: QNX cpu frequency scaling ?   
For example, newer AMD chips have a TSC_INVARIANT flag in their CPUID
features which indicates that TSC doesn't change during speedstep
operations.
But in older ones it did.
There are a million different stories out there...

Before we support this sort of thing we need to have a nice think about
it... 

Brian Stecher wrote: 

On Wed, Jan 16, 2008 at 12:12:14PM -0500, Attilla Danko wrote: 
> But it would probably good for the docs to list the boards/BSPs that break

> that 
> assumption. 
> 
> Would you know who I should ask? 

I don't think anyone "knows" - it's a matter of looking at the CPU's on each

of the board, then reading the chip doc to see if it does frequency 
scaling and figuring out if the ClockCycles() timer is affected by it and 
if we enable the frequency scaling feature in the BSP. 

        Brian 

-- 
Brian Stecher (bstecher@qnx.com <mailto:bstecher@qnx.com>; )        QNX
Software Systems 
phone: +1 (613) 591-0931 (voice)        175 Terence Matthews Cr. 
       +1 (613) 591-3579 (fax)          Kanata, Ontario, Canada K2M 1W8 

_______________________________________________ 
OSTech 
http://community.qnx.com/sf/go/post4367
<http://community.qnx.com/sf/go/post4367>;  


-- 

cburgess@qnx.com <mailto:cburgess@qnx.com>;

Return


  A subsidiary of BlackBerry             All content ©2004-2013, QNX Software Systems