Messages in this thread |  | | | Date | Fri, 22 Sep 2006 09:07:14 +0200 | | From | Ingo Molnar <> | | Subject | Re: [PATCH] Linux Kernel Markers 0.5 for Linux 2.6.17 (with probe management) |
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* Mathieu Desnoyers <compudj@krystal.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?
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