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Date: Fri, 12 Jun 2009 11:00:21 -0700 From: Corey Ashford <cjashfor@...ux.vnet.ibm.com> To: Paul Mackerras <paulus@...ba.org> CC: Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH 2/2] perf_counter: powerpc: Implement generalized cache events for POWER processors Paul Mackerras wrote: > Ingo Molnar writes: > > Yeah. > > When thinking about having "composite" events, i.e. a counter whose > value is computed from two or more hardware counters, I couldn't see > how to do sampling in the general case. It's easy if we're just > adding multiple counters, but sampling when subtracting counters is > hard. For example, if you want to sample every N cache hits, and > you're computing hits as accesses - misses, I couldn't see a decent > way to know when to take the sample, not without having to take an > interrupt on every access in some circumstances. The PAPI equivalent of this, its preset aka standard events, do not allow profiling or interrupt on overflow for "derived" events. "derived events" has the same meaning as your composite events. So there is precedent for not allowing sampling on them. Regards, - Corey Corey Ashford Software Engineer IBM Linux Technology Center, Linux Toolchain -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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