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

[Mathieu Desnoyers]

* 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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-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com