linux-kernel - Re: [RFC] The New and Improved Logdev (now with kprobes!)

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Message-ID: <Pine.LNX.4.58.0610051623520.432@gandalf.stny.rr.com>
Date:	Thu, 5 Oct 2006 16:26:39 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Daniel Walker <dwalker@...sta.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Karim Yaghmour <karim@...rsys.com>,
	Andrew Morton <akpm@...l.org>,
	Chris Wright <chrisw@...s-sol.org>, fche@...hat.com,
	Tom Zanussi <zanussi@...ibm.com>
Subject: Re: [RFC] The New and Improved Logdev (now with kprobes!)


On Thu, 5 Oct 2006, Mathieu Desnoyers wrote:

>
> Just as a detail : LTTng traces NMI, which can happen on top of a
> xtime_lock. So yes, I have to consider the impact of this kind of lock when I
> choose my time source, which is currently a per architecture TSC read,
> or a read of the jiffies counter when the architecture does not have a
> synchronised TSC over the CPUs. This is abstracted in include/asm-*/ltt.h.
>

I'm curious.  How do you show the interactions between two CPUs when the
TSC isn't in sync?  Using jiffies is not fast enough to know the order of
events that happen within usecs.

-- Steve


> I know it doesn't support dynamic ticks, I'm working on using the HRtimers
> instead, but I must make sure that the seqlock read will fail if it nests over
> a write seqlock.
>
> MAthieu
>
> OpenPGP public key:              http://krystal.dyndns.org:8080/key/compudj.gpg
> Key fingerprint:     8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
>
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