[ltt-dev] trace_clock_update() spinning

[Mathieu Desnoyers]

* Mike McTernan (mmcternan at airvana.com) wrote:
> * Mathieu Desnoyers wrote:
> > - Does your architecture support power management sleep modes ? If
> yes,
> > does the cycle counter stop in sleep modes ?
> > - Does your architecture support dynamic ferquency scaling ?
> 
> Yes and yes and yes.  So as per your paper on exotic embedded
> architectures it would need to use a timer to work out real time after a
> sleep period like on OMAP3.  Making that stuff generic (like the 32 to
> 64 code) would be great.
> 
> Luckily in my application we disable DVFS and power management so this
> is ok.

Could you update the patch so it uses the generic timestamp if DVFS or PM are
enabled in the kernel config ?

> 
> Alternatively i.MX51 has a programmable timer that runs reasonably fast
> (66.5MHz on my setup) and is independent of power saving.  It's called
> the EPIT, and I had that working too, but used the cycle count for
> greater resolution and for it's similarities with OMAP3.

Usually, anything that is outside of the CPU is terribly slow to read (memory
mapped I/O). So using the TSC seems to be the best solution.

> 
> > - Would you agree for me to integrate it in the lttng project and
> transfer
> > non-exclusive relicensing rights to the LTTng maintainer ? Basically,
> > the idea is to release it under dual GPLv2/LGPLv2.1 licenses, but I
> > start to think that it might be just easier to use the gdb approach
> for
> > LTTng contributions, where the project maintainers have the freedom to
> > decide license changes. 
>  
> The patch is small and unspecial.  I'd be happy to reassign the
> copyright in this case.  
> 
> > This way we would not have to ask permission from everyone if we need
> to
> > do a license change for the LTTng project overall.
> 
> I wouldn't be too happy with that if I were to submit something
> substantial.  

Well, I'm happy with whatever is the less trouble for everyone and ensures that
the code stays open. So GPLv2/LGPLv2.1 is fine. Just as a thought, if you
copy-pasted code from the other architectures into these headers, perharps it
would be better to leave the copyright notices already in place in addition to
yours. That would help copyright traceability. ;)

Thanks !

Mathieu


> 
> Kind Regards,
> 
> Mike