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Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)
- From: Ingo Molnar <mingo at elte dot hu>
- To: Mathieu Desnoyers <compudj at krystal dot dyndns dot org>
- Cc: Martin Bligh <mbligh at google dot com>, "Frank Ch. Eigler" <fche at redhat dot com>, Masami Hiramatsu <masami dot hiramatsu dot pt at hitachi dot com>, prasanna at in dot ibm dot com, Andrew Morton <akpm at osdl dot org>, 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: Fri, 22 Sep 2006 09:07:14 +0200
- Subject: Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management)
- References: <20060921160009.GA30115@Krystal> <20060921160656.GA24774@elte.hu> <20060921214248.GA10097@Krystal>
* Mathieu Desnoyers <email@example.com> wrote:
> I clearly expressed my position in the previous emails, so did you.
> You argued about a use of tracing that is not relevant to my vision of
> reality, which is :
> - Embedded systems developers won't want a breakpoint-based probe
are you arguing that i'm trying to force breakpoint-based probing on
you? I dont. In fact i explicitly mentioned that i'd accept and support
a 5-byte NOP in the body of the marker, in the following mails:
"just go for [...] the 5-NOP variant"
(my reply to your second proposal)
"or at most one NOP"
(my reply to your third proposal)
"at most a NOP inserted"
(my reply to your fifth proposal)
That enables the probe to be turned into a function call - not an INT3
breakpoint. Does it take some effort to implement that on your part?
Yes, of course, but getting code upstream is never easy, /especially/ in
cases where most of the users wont use a particular feature.
> - High performance computing users won't want a breakpoint-based probe
I am not forcing breakpoint-based probing, at all. I dont want _static,
build-time function call based_ probing, and there is a big difference.
And one reason why i want to avoid "static, build-time function call
based probing" is because high-performance computing users dont want any
overhead at all in the kernel fastpath.
> - djprobe is far away from being in an acceptable state on
> architectures with very inconvenient erratas (x86).
djprobes over a NOP marker are perfectly usable and safe: just add a
simple constraint to them to only allow a djprobes insertion if it
replaces a 5-byte NOP.
> - kprobe and djprobe cannot access local variables in every cases
it is possible with the marker mechanism i outlined before:
have i missed to address any concern of yours?