[ltt-dev] trace_clock_update() spinning
mathieu.desnoyers at efficios.com
Tue Feb 9 09:42:37 EST 2010
* Mike McTernan (mmcternan at airvana.com) wrote:
> * Mathieu Desnoyers wrote:
> > * Mike McTernan (mmcternan at airvana.com) wrote:
> > > Luckily in my application we disable DVFS and power management so
> > > is ok.
> > Could you update the patch so it uses the generic timestamp if DVFS or
> > are enabled in the kernel config ?
> I would like to say yes, but in truth I have neither the time or means
> to test this. Note I didn't submit the patch requesting inclusion,
> merely to perhaps help others considering use of LTTng on iMX51's and
> That said, I passed the patch to Freescale and asked that they consider
> getting LTTng supported in their BSP as it is such an excellent tool.
Yep, I understand your time constraints. Thanks for passing this on to
> > > Alternatively i.MX51 has a programmable timer that runs reasonably
> > > (66.5MHz on my setup) and is independent of power saving. It's
> > > 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.
> I agree that the TSC is better, also because its use could be
> generalised for all ARM Cortex A8's and probably later ARMs.
> > Well, I'm happy with whatever is the less trouble for everyone and
> > that the code stays open. So GPLv2/LGPLv2.1 is fine.
> That's a good outlook & keeping it GPL or LGPL is cool. My only worry
> about reassignment would be that a future version could be under a less
> permissive license.
> > Just as a thought, if you copy-pasted code from the other
> > into these headers, perharps it would be better to leave the copyright
> > notices already in place in addition to yours. That would help
> > traceability. ;)
> The assembly is derivative from the ARM reference, which will be the
> same on every Cortex A8 (bar chip errata like the broken bit 31 on
> The empty functions to complete the interface follow from the generic
> implementation, as they must in order to compile. The mutex & reference
> count to safely enable/disable the clock is the same as the generic
> code; I should probably credit you for those 8 lines.
Well, if it's "trivial", then credits are unnecessary, but I've always stayed on
the safe side license-wise. It makes it easier in the future if we have to dig
back into these patches.
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