linux-kernel - Re: [RFC][BUG] tracer: Fails to work

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Message-ID: <1616014588.6697.1453991896740.JavaMail.zimbra@efficios.com>
Date:	Thu, 28 Jan 2016 14:38:16 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [RFC][BUG] tracer: Fails to work

----- On Jan 28, 2016, at 8:57 AM, Peter Zijlstra peterz@...radead.org wrote:

> On Thu, Jan 28, 2016 at 01:38:00PM +0000, Mathieu Desnoyers wrote:
> 
>> Thoughts ?
> 
> So ideally dumping the trace data would not depend on any of that,
> because I can break it all :-)
> 
> Not being able to access the trace data completely and utterly defeats
> the purpose of having a tracer in the first place.

One item I have on my todo list is to allow mapping
the tracer buffers (lttng in my case) onto RAM that
persists across reboots/kexec using dax and the pmem
driver. Since the original system is clearly inactive
after a reboot, we can read the buffers from memory
without caring about synchronization.

That would be one possible way of handling your
snapshot-of-buggy-kernel-trace-buffers use-case.

Thanks,

Mathieu

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com