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

David Ahern
2011-03-03T14:33:08Z

On 03/03/2011 01:51 AM, Ingo Molnar wrote:
>
> * David Ahern <daahern@cisco.com> wrote:
>
>>> How does all that deal with CLOCK_REALTIME being affected by NTP and
>>> settimeofday? Not really, as far as I can tell. It somehow works, but
>>> that depends on the frequency of your event injection.
>>
>> It is sampled at some periodic rate to get NTP changes. Right now it is
>> hardcoded at once an hour. The frequency option can be added to the
>> --tod parameter.
>
> As Thomas mentioned, we probably need something more complete than that.

Just responded to Thomas' email with a simpler proposal than munging on
tracepoints and trying to track time-of-day implicitly.

> Still your approach is obviously useful and i'd like to stress that explicitly. Have

Thanks for stating that.

> you considered another related feature, feeding printk lines as special 'string
> events' into the perf ringbuffer?
>
> It would round up your scheme very nicely: that way you'd have a single, global,
> GTOD-correlated event store/flow for basically every system event you might be
> interested in. You could switch events (and tracepoints) on/off based on need,
> controlling the type and rate of information in a very finegrained way.
>
> If the printk approach works out i'd even suggest that such a facility would need a
> separate tool within perf: 'perf syslog' or 'perf log'. It would heavily reuse
> perf-script and other perf internal facilities, obviously - but you would not be
> tied to any particular sub-tool implementation.
>
> EDAC type events could feed into this as well, giving the tool a broader 'system
> health' aspect as well, beyond the 'system performance analysis' aspect.

I can look into it (as time allows) once I get the dumping of software
events done.

David

>
> Thanks,
>
> Ingo