Re: [PATCH 3/6] perf record: add time-of-day option

David Ahern
2011-03-01T22:35:23Z

On 03/01/2011 03:28 PM, Peter Zijlstra wrote:

>> And for some silly reason I sense a time trap here (pun intended) .....
>>
>> So your pushback is:
>> 1. throw out the realtime-clock event patch,
>
> Well, no, you need continues samples to keep in sync, so having this is
> required [*].
>
>> 2. add a new CLOCK_TRACING type to clock_gettime with VDSO hook,
>
> Right, that is something we need anyway at some point in time.
>
>> 3. and use a synthesized event from userspace for snapshotting
>> perf_clock to time-of-day -- similar to what I have now, but one that
>> will guarantee a time-of-day to perf_clock correlation (versus the
>> current one which hopes that perf_clock is the monotonic clock).
>
> I guess you could do that if we have full userspace tracing support, but
> it wouldn't need synthesized events, it would need a pure userspace
> event stream.

I still don't see how this solves the need to trigger the initial sample
into the event stream.

David

>
> Thing is, I really dislike the ioctl() trigger
>
>
>