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

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Date:	Thu, 03 Mar 2011 07:33:24 -0700
From:	David Ahern <daahern@...co.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	linux-perf-users@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, acme@...stprotocols.net,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	John Stultz <johnstul@...ibm.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 3/6] perf record: add time-of-day option



On 03/03/2011 01:51 AM, Ingo Molnar wrote:
> 
> * David Ahern <daahern@...co.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
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