Messages in this thread | | | Date | Fri, 8 Jul 2011 01:00:59 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH v2] trace: Add x86 irq vector entry/exit tracepoints |
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On Thu, Jul 07, 2011 at 03:50:04PM -0700, David Sharp wrote: > On Thu, Jul 7, 2011 at 2:57 AM, Ingo Molnar <mingo@elte.hu> wrote: > > > > * H. Peter Anvin <hpa@zytor.com> wrote: > > > >> Yes, it was much more of a generic concern. However, it is very > >> important that people have a correct idea about what the stability > >> of something like tracepoint is -- or we'll end up in a situation > >> where we can never change the kernel because anything is suddenly > >> "user space visible." > > > > We've transitioned even ABI-assuming tracepoints in the past, so it's > > not a big issue in practice. The reason is that this is an atypical > > type of ABI: information is read-only exported, for observation > > purposes. > > > > If the kernel changes in a fundamental way that removes a tracepoint > > altogether, then there's nothing left to observe - so apps don't > > break per se. > > > > So i've yet to see a single example of the kernel 'never being able > > to change' due to a tracepoint. The worst we've seen in practice is > > the inability to change a specific tracepoint (not the surrounding > > kernel code - while preserving the information that is exposed) - so > > the worst effect was limited to tracing itself - never to the > > subsystem that it traces. > > > > Note that even in that (single known) example we were able to resolve > > the problem (which was limited to the tracing subsystem) by adding > > new tracepoints and thus phasing out the old ones. > > > > Thanks, > > > > Ingo > > > > Thanks all for your thorough review. :) It sounds like there is some > agreement now. I think this Steve is waiting for an Acked-by from an > x86 maintainer to apply this patch. Are there any further objections > or comments on the patch?
Yeah I have some comments on it. I just postponed my reply because I did not have clear suggestions to propose back until now.
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