2.6.13 new option timer frequency

2.6.13 new option timer frequency

[Nick Warne]

Hi all,

I built and installed 2.6.13 today, and oldconfig revealed the new option for 
timer frequency.

I searched the LKML on this, but all I found is the technical stuff - not 
really any layman solutions.

Two n00b questions here:

What does this do/what is it for?

I selected default, 250Hz.  If this is now an option, what was it before?

Thanks,

Nick
-- 
"When you're chewing on life's gristle,
Don't grumble, Give a whistle..."

Re: 2.6.13 new option timer frequency

[Lee Revell]

On Mon, 2005-08-29 at 18:57 +0100, Nick Warne wrote:
> Hi all,
> 
> I built and installed 2.6.13 today, and oldconfig revealed the new option for 
> timer frequency.
> 
> I searched the LKML on this, but all I found is the technical stuff - not 
> really any layman solutions.
> 
> Two n00b questions here:
> 
> What does this do/what is it for?
> 

Selects the frequency of the timer interrupt.  This controls the timing
resolution of system calls.  So previously poll/select could be used
with a 1ms timeout.  Now with the default settings it can only do 4ms. 

> I selected default, 250Hz.  If this is now an option, what was it before?

The previous value was 1000HZ.  And yes, changing the default from 1000
to 250 breaks the expected "make oldconfig" behavior.  Lots of people
are not happy about it, but were overruled by Linus.

Lee

Re: 2.6.13 new option timer frequency

[Maciej Soltysiak]

Hi,

> Two n00b questions here:
> What does this do/what is it for?
I'm no guru, but its something like the resolution of the timer the kernel
runs. More Hz give you shorter timeslices and lower latency. Lower give
longer timeslices and higher latency.

Anybody please correct me if I am wrong here.

> I selected default, 250Hz.  If this is now an option, what was it before?
AFAIK previously we've had here 1000Hz.


Basically, for a server you'd want 100.
For a desktop 250
For a low-latency (eg. working on audio) you'd want 1000

Again, correct me if I am wrong.

Regards,
Maciej

Re: 2.6.13 new option timer frequency

[Jonathan Corbet]

> I built and installed 2.6.13 today, and oldconfig revealed the new option for 
> timer frequency.
> 
> I searched the LKML on this, but all I found is the technical stuff - not 
> really any layman solutions.

I wrote a bit about the timer frequency option a few weeks ago:

	http://lwn.net/Articles/145973/

jon

Jonathan Corbet
Executive editor, LWN.net
corbet@lwn.net

Re: 2.6.13 new option timer frequency

[Nick Warne]

On Monday 29 August 2005 19:48, Jonathan Corbet wrote:
> > I built and installed 2.6.13 today, and oldconfig revealed the new option
> > for timer frequency.
> >
> > I searched the LKML on this, but all I found is the technical stuff - not
> > really any layman solutions.
>
> I wrote a bit about the timer frequency option a few weeks ago:
>
> 	http://lwn.net/Articles/145973/

OK, thanks everybody for replies.

Jon, that is a near perfect article - I understand it all now.

I haven't noticed anything different under 250HZ yet..., if anything machine 
seems smoother.  Lower electricity bills will be handy as well ;-)

Thanks,

Nick
-- 
"When you're chewing on life's gristle,
Don't grumble, Give a whistle..."

Re: 2.6.13 new option timer frequency

[Lee Revell]

On Mon, 2005-08-29 at 12:48 -0600, Jonathan Corbet wrote:
> > I built and installed 2.6.13 today, and oldconfig revealed the new option for 
> > timer frequency.
> > 
> > I searched the LKML on this, but all I found is the technical stuff - not 
> > really any layman solutions.
> 
> I wrote a bit about the timer frequency option a few weeks ago:
> 
> 	http://lwn.net/Articles/145973/
> 

I just updated the thread to explain the "singing capacitor" issue which
has been mostly overlooked in this debate so far.

Lee