linuxaudio.org

On May 4, 2011 08:20:51 pm you wrote:

quoted text
> On Wed, May 4, 2011 at 7:11 PM, Tim E. Real  wrote:

> > I discovered gettimeofday occasionally gives me a time value

> >  which is less than a previous time value. The value is actually

> >  'out of order' and really belongs ahead of a few others,

> >  according to examined printouts.

> >

> > So I tried  clock_gettime(CLOCK_MONOTONIC, ..), same result.

>

> i believe you want CLOCK_REALTIME. however, if CLOCK_MONOTONIC is

> malfunctioning and you can prove it with a very small piece of code,

> the kernel guys will want to know.

>

> > Still checking some things, maybe there's a reason, the app's fault.

> > From what I've read gettimeofday is thread safe, but the incorrect

> >  time values are being read by the same thread always.

>

> gettimeofday() is subject to system time corrections (e.g. via NTP).

> it is never ever guaranteed to be monotonic.

Weird, CLOCK_REALTIME does it too.

Only CLOCK_PROCESS_CPUTIME_ID does not.
Been reading, according to places like this:
http://stackoverflow.com/questions/3523442/difference-between-clock-real...

and-clock-monotonic
http://stackoverflow.com/questions/3657289/linux-clock-gettimeclock-mono...

strange-non-monotonic-behavior
CLOCK_MONOTONIC and CLOCK_MONOTONIC_RAW are not supposed to go backwards

 but apparently CLOCK_MONOTONIC just might and CLOCK_MONOTONIC_RAW is better,

 and CLOCK_REALTIME is less reliable than that.
However on that second page it mentions a kernel fix, more recent than mine.

Mine also doesn't seem to have CLOCK_MONOTONIC_RAW.
I am going to chalk it up to this older kernel, and test on my newer machine

 and hope it vanishes...
In the meantime, I can make the code I'm working on tolerant.

I'm just not sure how this affects the rest of the existing app code -

 could this be the source of occasional bugs or have we just been lucky or

 is it already tolerant...
Thanks!
_______________________________________________

Linux-audio-dev mailing list

Linux-audio-dev@lists.linuxaudio.org

http://lists.linuxaudio.org/listinfo/linux-audio-dev