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

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Message-Id: <1160074147.6660.10.camel@c-67-180-230-165.hsd1.ca.comcast.net>
Date:	Thu, 05 Oct 2006 11:49:06 -0700
From:	Daniel Walker <dwalker@...sta.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	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, 2006-10-05 at 14:38 -0400, Steven Rostedt wrote:
> On Thu, 5 Oct 2006, Daniel Walker wrote:
> 
> > On Thu, 2006-10-05 at 14:09 -0400, Steven Rostedt wrote:
> >
> > >
> > > My problem with using a timestamp, is that I ran logdev on too many archs.
> > > So I need to have a timestamp that I can get to that is always reliable.
> > > How does LTTng get the time for different archs?  Does it have separate
> > > code for each arch?
> > >
> >
> > I just got done updating a patchset that exposes the clocksources from
> > generic time to take low level time stamps.. But even without that you
> > can just call gettimeofday() directly to get a timestamp .
> >
> 
> unless you're tracing something that his holding the xtime_lock ;-)

That's part of the reason for the changes that I made to the clocksource
API . It makes it so instrumentation, with other things, can generically
read a low level cycle clock. Like on PPC you would read the
decrementer, and on x86 you would read the TSC . However, the
application has no idea what it's reading.

I submitted one version to LKML already, but I'm planning to submit
another version shortly.

Daniel

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