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Author Topic: Timer resolution  (Read 6779 times)

Offline Tuftec

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Re: Timer resolution
« Reply #15 on: June 07, 2011, 07:39:14 PM »
Yep using a DMP SOC system.

So what timers exactly does TC look for.
The DMP chip has 2 x 8254 style timers on board (same as a regular PC I believe).
I will check a bit closer to find how their resolution is set. But I would suspect this is an OS setup thing.

I will look at the force option.



Offline Tuftec

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Re: Timer resolution
« Reply #16 on: June 07, 2011, 07:52:02 PM »
Ah yes!!!!

I have just done some reading. The 8254 timer implementation is the problem.
For HPET (and hence HRT) the timers need to be 8253 type.

I guess I could drop the tick (jiffie) time down to 1ms for a marginal improvement but 3 x as many interrupts and probably some sacrifice in performance.

Changing the hardware is not my preference at this point.

Is there an easy way to experiment with different jiffie times? Maybe a boot option or modprobe command or something?

Offline curaga

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Re: Timer resolution
« Reply #17 on: June 08, 2011, 09:57:08 AM »
No, I don't think they can be set any other way than build time. Many compile-time constants depend on the value.
The only barriers that can stop you are the ones you create yourself.

Online Rich

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Re: Timer resolution
« Reply #18 on: June 08, 2011, 10:51:47 AM »
Hi Tuftec
Go to this link
http://www.mjmwired.net/kernel/Documentation/kernel-parameters.txt
and search that page for the word  jif
You will find 2 possibilities for changing the kernel's timing. Don't be to aggressive with timing changes.
Linux was not designed to do context changes every few microseconds.

Offline Tuftec

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Re: Timer resolution
« Reply #19 on: June 09, 2011, 03:59:09 AM »
Thanks

Online Rich

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Re: Timer resolution
« Reply #20 on: June 09, 2011, 01:07:51 PM »
Hi Tuftec

By the way, the link I provided you is chock full of information. You do however need to dig a bit and
get your hands dirty to find some of it. The column on the left includes other subjects such as
scheduler. And as an example of digging, there is some more information about scheduling under
the subject  Block.