[ltt-dev] trace-clock-userspace.patch for ARM/PowerPC ?

[Abbas Raza]

On 07/19/2011 08:18 PM, Mathieu Desnoyers wrote:
> * Abbas Raza (abbas_raza at mentor.com) wrote:
>> On 07/15/2011 12:05 PM, Abbas Raza wrote:
>>> Hello guys,
>>>
>>> There is a patch "trace-clock-userspace.patch" (available on 2.6.36)
>>> that syncs the clock so that both kernel and userspace trace sets are
>>> in perfect time sync. Currently this patch is only for x86
>>> architecture.
>>> Any idea or info that when this patch will be available for
>>> ARM/PowerPc architectures? Is this expected in next lttng patch
>>> releases?
>>>
>>> Thanks!
>>>
>>> Regards,
>>>
>>> Abbas Raza
>>>
>> Or can anyone give me some direction how to extend clock_gettime vdso to
>> read lttng trace clock from userspace for other architectures ARM/PowePc
>> ?
> Hi Abbas,
>
> The LTTng development is currently done on LTTng pre-2.0, in preparation
> for the upcoming 2.0 release. There is no plan to add features to the
> LTTng 0.x versions anymore (it is only in bugfix maintainance mode).
>
> As far as trace clocks are concerned, LTTng 2.0 currently uses the Linux
> kernel time source (temporary fallback, which is slower than lttng trace
> clocks, less precise and not nmi-reentrant). The plan is to merge the
> LTTng 0.x trace clocks into the LTTng 2.0 kernel modules
> (lttng-modules.git tree) and present them to userspace through a custom
> vDSO (a shared memory page allocated from a lttng-specific ioctl on the
> debugfs "lttng" file). The same page can be shared across all processes
> calling this ioctl. Its main purpose is to expose information from the
> kernel to userspace: typically a sequence lock and some data structure
> (either global and/or per-cpu) to show how e.g. to extend a 31-bit cycle
> counter to a 64-bit value, how to scale the cycle counter value to a
> reference frequency, etc.
>
> So if you want to help out, a first step would be to get the latest
> lttng 0.x trace clock code for all architectures and integrate it into
> lttng-modules.git master branch. Then, after this, we can focus on
> getting the vDSO to work.
>
> I'm currently busy working on LTTng-UST 2.0 (the userspace tracer part),
> which should be ready by the end of the summer. LTTng 2.0 kernel tracer
> works today, so we plan to do a pre-2.0 release soon (just for the
> kernel tracer and the lttng-tools control tools).
>
> Thanks!
>
> Mathieu
>
>> Thanks!
>>
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>>
Hello,

Thanks a lot for reply !

Just wanted to ask that which time source is used in LTTng 0.x for 
kernel traces? As far as i know it uses trace clock which in turn use 
TSC (in case of x86).
Is it right? And thats the reason that since TSC is used for kernel 
traces, so we must use the same for userspace traces to sync them up? 
And for PowerPc instead of TSC, Time Base TB will be used?
Am i getting things right?

Thanks!

Abbas Raza