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Re: [PATCH] Linux Kernel Markers
- From: Karim Yaghmour <karim at opersys dot com>
- To: "Frank Ch. Eigler" <fche at redhat dot com>
- Cc: Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, Martin Bligh <mbligh at google dot com>, prasanna at in dot ibm dot com, Andrew Morton <akpm at osdl dot org>, Ingo Molnar <mingo at elte dot hu>, Mathieu Desnoyers <mathieu dot desnoyers at polymtl dot ca>, Paul Mundt <lethal at linux-sh dot org>, linux-kernel <linux-kernel at vger dot kernel dot org>, Jes Sorensen <jes at sgi dot com>, Tom Zanussi <zanussi at us dot ibm dot com>, Richard J Moore <richardj_moore at uk dot ibm dot com>, Michel Dagenais <michel dot dagenais at polymtl dot ca>, Christoph Hellwig <hch at infradead dot org>, Greg Kroah-Hartman <gregkh at suse dot de>, Thomas Gleixner <tglx at linutronix dot de>, William Cohen <wcohen at redhat dot com>, ltt-dev at shafik dot org, systemtap at sources dot redhat dot com, Alan Cox <alan at lxorguk dot ukuu dot org dot uk>
- Date: Wed, 20 Sep 2006 14:25:41 -0400
- Subject: Re: [PATCH] Linux Kernel Markers
- Organization: Opersys inc.
- References: <4510151B.5070304@google.com> <20060919093935.4ddcefc3.akpm@osdl.org> <45101DBA.7000901@google.com> <20060919063821.GB23836@in.ibm.com> <45102641.7000101@google.com> <20060919070516.GD23836@in.ibm.com> <451030A6.6040801@google.com> <45105B5E.9080107@opersys.com> <451141B1.40803@hitachi.com> <451178B0.9030205@opersys.com> <20060920180808.GI18646@redhat.com>
- Reply-to: karim at opersys dot com
Hello Frank,
Frank Ch. Eigler wrote:
> My interpretation of Martin's Monday proposal is that, if implemented,
> we wouldn't need any of this nop/int3 stuff. If function being
> instrumented were recompiled on-the-fly, then it could sport plain &
> direct C-level calls to the instrumentation handlers.
Absolutely. I guess the length of these threads is just fertile
ground for misunderstandings. Basically what Hiramatsu-san and
myself were discussing was just the mechanism for selecting/
forking in between the uninstrumented function and the instrumented
one.
So, to recap:
If you had 100,000 instrumentation points in the scheduler (obviously
a totally bogus number here ...) you'd have 2 functions:
1- one with no instrumentation at all, but with a 5byte filler such
as the one presented by Hiramatsu-san.
2- one with the instrumentation.
Early in the proposal, the mechanics of switching in between "1" and "2"
seemed to be problematic, but I think with Hiramatsu-san's proposal
and, on the x86, djprobes, we've got it figured out.
Let me know if I'm not providing enough detail.
Thanks,
Karim