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Date: Fri, 22 Sep 2006 09:07:14 +0200 From: Ingo Molnar <mingo@...e.hu> To: Mathieu Desnoyers <compudj@...stal.dyndns.org> Cc: Martin Bligh <mbligh@...gle.com>, "Frank Ch. Eigler" <fche@...hat.com>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, prasanna@...ibm.com, Andrew Morton <akpm@...l.org>, Paul Mundt <lethal@...ux-sh.org>, linux-kernel <linux-kernel@...r.kernel.org>, Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>, Richard J Moore <richardj_moore@...ibm.com>, Michel Dagenais <michel.dagenais@...ymtl.ca>, Christoph Hellwig <hch@...radead.org>, Greg Kroah-Hartman <gregkh@...e.de>, Thomas Gleixner <tglx@...utronix.de>, William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org, systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk> Subject: Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management) * Mathieu Desnoyers <compudj@...stal.dyndns.org> 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" http://marc.theaimsgroup.com/?l=linux-kernel&m=115859771924187&w=2 (my reply to your second proposal) "or at most one NOP" http://marc.theaimsgroup.com/?l=linux-kernel&m=115865412332230&w=2 (my reply to your third proposal) "at most a NOP inserted" http://marc.theaimsgroup.com/?l=linux-kernel&m=115886524224874&w=2 (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: http://marc.theaimsgroup.com/?l=linux-kernel&m=115886524224874&w=2 have i missed to address any concern of yours? Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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