Re: [PATCH 10/11] tracing/perf: Fix lock events recursions in thefast path

[Peter Zijlstra]

On Fri, 2010-02-05 at 13:10 +0100, Peter Zijlstra wrote:
> On Fri, 2010-02-05 at 11:49 +0100, Ingo Molnar wrote:
> > 
> > > That said, I'm not at all happy about removing lockdep annotations to make 
> > > the tracer faster, that's really counter productive.
> > 
> > Are there no dynamic techniques that could be used here?
> > 
> > Lockdep obviously wants maximum instrumentation coverage - performance be 
> > damned.
> > 
> > Lock profiling/tracing/visualization wants the minimum subset of events it is 
> > interested in - everything else is unnecessary overhead.
> 
> Well, they could start by moving the tracepoint inside the lockdep
> recursion check.

IIRC the reason its now outside is that you'd loose tracepoint on
lockdep_off() usage, but having the tracer folks help on removing any
such usage is of course a good thing.

The usage thereof in nmi_enter() doesn't seem like a problem, since
you're not supposed to be using locks from nmi context anyway, more so,
I'd not be adverse to putting BUG_ON(in_nmi()) in every lockdep hook.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/