linux-kernel - Re: [patch] trace: Add user-space event tracing/injection

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Date:	Wed, 17 Nov 2010 14:33:14 +0200
From:	Pekka Enberg <penberg@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Darren Hart <dvhart@...ux.intel.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [patch] trace: Add user-space event tracing/injection

On 11/17/10 2:30 PM, Ingo Molnar wrote:
> What does the duration in milliseconds mean there? For things like
>> GC and JIT, I want something like:
>>
>> void gc(void)
>> {
>>          prctl(PR_TASK_PERF_USER_TRACE_START, ...)
>>
>>          collect();
>>
>>          prctl(PR_TASK_PERF_USER_TRACE_END, ...)
>> }
>>
>> So that it's clear from the tracing output that the VM was busy
>> doing GC for n milliseconds. Barring background JIT'ing and
>> pauseless GC, I'd also be interested in showing how much time the VM
>> was actually _blocking_ the running application (which can happen
>> with signals too, btw, for things like accessing data that's lazily
>> initialized).
> We can add two events: user_event_entry/user_event_exit - or we could use the string
> to differentiate, and start it with:
>
>    "entry: ..."
>    "exit: ..."
>
> And then the event timestamps (which are absolute and are available) could be used
> to calculate the duration of this period.
>
> 'trace' could even be taught to treat such entry:/exit: strings in a special way, so
> that you dont have to write Jato specific trace decoding bits?

Yes, makes sense. I like the API so lets convince others that it's 
important enough to be merged. :-)

             Pekka
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