Messages in this thread | | | Date | Thu, 21 Jul 2011 15:03:38 +0200 | From | Frederic Weisbecker <> | Subject | Re: [PATCH 3/6] x86: Allow the user not to build hw_breakpoints |
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On Thu, Jul 21, 2011 at 09:26:56AM +0200, Ingo Molnar wrote: > > * H. Peter Anvin <hpa@zytor.com> wrote: > > > On 07/14/2011 08:03 AM, Frederic Weisbecker wrote: > > > So that hw_breakpoints and perf can be not built on > > > specific embedded systems. > > > > I want to emphasize I am very, very unhappy about this. It should > > be possible to not build perf while still have breakpoints > > available... breakpoints are way more important than perf. > > What we could indeed do is to separate out a 'core perf' portion that > is necessary for hw-breakpoints to work fine, thus allowing for > example the PMU drivers to be disabled.
That would still require a big chunk of perf.
> > Otherwise we have expressed hw breakpoint APIs via perf events and > that model is working well. Making hw-breakpoints a separate > subsystem again with isolated (and partly duplicated) infrastructure > would be a step back really.
I actually don't think it's working well. What we have with the current design is the dependency to perf as a big midlayer that is apparently convenient but actually induce some nasty things.
Just look how we need those ptrace_get_breakpoints() protection to deal with perf exit path implementation for example. Or the need for archs to translate arch ptrace breakpoint info into generic perf attrs.
I think we had to try the current design just to see if that could plug nicely. But now that we have this for several releases, I can only conclude that we should revert back to the design Prasad proposed, consisting in having breakpoints a service used by perf but not the opposite.
For ptrace, all it takes is a generic hook in the preempt notifiers to activate/deactivate breakpoints. I much prefer that to a big dependency on a perf core midlayer.
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