Messages in this thread | | | Date | Wed, 29 Jul 2009 02:36:09 +0200 | From | Frederic Weisbecker <> | Subject | Re: [RFC][PATCH 5/5] perfcounter: Add support for kernel hardware breakpoints |
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On Tue, Jul 28, 2009 at 09:24:37AM +0200, Peter Zijlstra wrote: > On Tue, 2009-07-28 at 03:03 +0200, Frederic Weisbecker wrote: > > > Thirdly, we can multiplex perf counters beyond their hardware maximum, > > > something you simply cannot do for a debug interface. > > > > > > Again, I'm stuck in what you mean by multiplexing here :-) > > If you'd create say 16 breakpoint counters, we'd RR them over the 4 > available hardware breakpoints (or less when others are taken by someone > else). > > Since its all statistics anyway, we can simply scale the event counts up > by the time-share they received. >
Aah, ok I understand now. But I fear it may kill the accuracy of the breakpoints statistics. It's fine for a theoretical linear rate of breakpoint events. But what happens if we are profiling something much more unstable with a rain of hits in a small window of memory between large timeframes? If we have a breakpoint inside this window of memory and this breakpoint is not plugged, waiting for its turn in the RR, we loose this rain of events.
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