CONFIG_PREEMPT and High Resolution Timers problem

CONFIG_PREEMPT and High Resolution Timers problem

[Vijay Nikam]

Hello All,
I have mpc8313erdb eval board with Linux-2.6.20 running on it.
Recently I had a problem, I wrote a driver and from I am sending
notification to user space application using fasync driver method
(SIGIO signal). In user space applicaion process I have used
posix-timers (timer_create and timer_settime), the timer is set for
10ms. But in actual I checked on oscilloscope the expiration of timer
or signal event generation varies between 10ms - 13ms. In kerenl
driver when the interrupt occurs I am making a gpio pin high and on
the signal event when timer expires I am making another gpio pin high,
and the time between these measured varies between 10ms - 13ms i.e. it
means the timer frequency is 250Hz, which was set by default for
powerpc. So to achieve close to precise of 10ms I set the timer
frequency to 1000Hz and then I got the resolution of 10ms -10.8ms.
I would like to ask is the right approach of changing Timer Frequency
to 1000Hz from 250Hz ? ? ?
Because while searching some information regarding this I learned
about High-Res Timers. In linux-2.6.20 x86 has this feature enabled
rather you can enable it but not for powerpc arch, Right ? ? ? If yes
then is there any way to add CONFIG_HIGH_RES_TIMERS feature to
linux-2.6.20, any patch available ? ? ? =A0otherwise what could be the
option ? ? ?

In Linux by default Preemption is not enabled, CONFIG_PREEMPT_NONE=3Dy
so I tried to enabled CONFIG_PREEMPT=3Dy but when I boot the board with
preemption enabled I got the scheduling with atomic error (please
check the log below, thanks). I tried to debug and find some info but
no luck. Could anyone please explain the reason for it and how I can
fix it ? ? ?

Kindly please acknowledge ... thank you ...

Kind Regards,
Vijay Nikam

########################### Start #################################
NET: Registered protocol family 1
NET: Registered protocol family 17
BUG: scheduling while atomic: swapper/0x00000001/1
Call Trace:
[C07F5D50] [C0008938] =A0(unreliable)
[C07F5D80] [C02933CC]
[C07F5DD0] [C029472C]
[C07F5E10] [C0201AF0]
[C07F5E50] [C0201E08]
[C07F5E90] [C01FEE14]
[C07F5EB0] [C0202018]
[C07F5F30] [C0017490]
[C07F5F50] [C02FB4B0]
[C07F5F90] [C0003960]
[C07F5FF0] [C0010C74]
BUG: scheduling while atomic: swapper/0x00000001/1
########################## END ####################################
########################## Start ####################################
BUG: scheduling while atomic: jffs2_gcd_mtd4/0x00000004/719
Call Trace:
[C05BDBE0] [C0008938] =A0(unreliable)
[C05BDC10] [C02933CC]
[C05BDC60] [C029472C]
[C05BDCA0] [C01D9F14]
[C05BDCE0] [C01D5424]
[C05BDD40] [C01D74D4]
[C05BDD70] [C01C9330]
[C05BDD80] [C0127F88]
[C05BDDB0] [C011F26C]
[C05BDE20] [C0120320]
[C05BDE90] [C012327C]
--- Exception: 1[C05BDF50] [C0125F0C] =A0(unreliable)
[C05BDFF0] [C0010C74]
######################## END ########################################

Re: CONFIG_PREEMPT and High Resolution Timers problem

[Tony Breeds]

On Sat, Apr 04, 2009 at 05:46:38PM +0530, Vijay Nikam wrote:

Hello Vijay.

> Because while searching some information regarding this I learned
> about High-Res Timers. In linux-2.6.20 x86 has this feature enabled
> rather you can enable it but not for powerpc arch, Right ? ? ? If yes
> then is there any way to add CONFIG_HIGH_RES_TIMERS feature to
> linux-2.6.20, any patch available ? ? ?  otherwise what could be the
> option ? ? ?

Getting high res times wrkign in 2.6.20 will be painful, the easyest option to
get HR timers wouyld be to grab 2.6.24 (or newer).  Of course that may cause
other pain for you.

Yours Tony