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Date: Wed, 17 Nov 2010 14:33:14 +0200
From: Pekka Enberg <penberg@kernel.org>
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To: Ingo Molnar <mingo@elte.hu>
CC: Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Steven Rostedt <rostedt@goodmis.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Darren Hart <dvhart@linux.intel.com>,
        Arjan van de Ven <arjan@infradead.org>
Subject: Re: [patch] trace: Add user-space event tracing/injection
References: <alpine.LFD.2.00.1011162103580.2900@localhost6.localdomain6> <4CE38C53.8090606@kernel.org> <20101117120740.GA24972@elte.hu> <4CE3C7C2.7000200@kernel.org> <20101117123055.GA27063@elte.hu>
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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