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Re: [PerfSuite-users] CPU time greater than Wall clock time
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From: Naveen P. <nav...@gm...> - 2009-01-05 21:52:34
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Rick, Thanks for the quick response and suggestions. It seems like a bug in Perfsuite and not PAPI. Here are the numbers for PAPI_TOT_CYC from a small test program. Using Perfsuite libpshwpc <http://perfsuite.ncsa.uiuc.edu/libpshwpc/> : 31,257,943,365 Using PAPI high-level interface: 8,628,425,548 Please note that ps_hwpc_start() and ps_hwpc_suspend() are called thousands of times within a large program to benchmark a specific function. The time granularity of this function is very small and hence, I have been using rdtsc to get independent timing measurements. The timing measurement using independent rdtsc are closer to one measured directly using PAPI. I also observed similar behavior with PAPI_TOT_INS, so it is likely that this bug is potentially influencing other events as well. I do not mind investing some time in finding this bug and fixing it in Perfsuite code base and will appreciate if you can tell me the potential places where I should be looking. -Naveen On Mon, Jan 5, 2009 at 3:30 PM, Rick Kufrin <rk...@nc...> wrote: > Naveen, > > Thanks for sending the document. We (of course) get the same results from > post-processing it here as you do, but cannot easily reproduce this behavior > with our own executables/tests on systems we have available. > > There are two suggestions I can think of to try offhand: > > 1. Add the "time" command to your run, i.e. "time psrun a.out", to get a > 3rd-party opinion of the wall clock and CPU time > > 2. PerfSuite supports using the "gettimeofday" system call for wall-clock > timing (by default, on a machine like yours, it uses the "rdtsc" asm > instruction). To use gettimeofday, one has to reconfigure PerfSuits with > the option "--enable-rtc=gettimeofday". Then make clean and remake as > normal. > > If you come across any more info looking into this, we are of course very > interested to address. Thanks for reporting. > > Rick > > Naveen Parihar wrote: > >> RIck, >> >> The XML document is attached with this email. I'm trying to debug the >> problem by directly using high-level PAPI interface. Will let you know my >> findings later. >> >> -Naveen >> >> On Mon, Jan 5, 2009 at 2:00 PM, Rick Kufrin <rk...@nc...<mailto: >> rk...@nc...>> wrote: >> >> Naveen, >> >> That certainly does sound like a bug, or at least unexpected >> behavior... >> >> Would you please send a copy of the XML document that you used to >> obtain this output? It may help to look at its contents closer to >> track down what is going on. >> >> Rick >> >> Naveen Parihar wrote: >> >> Dear Perfsuite users, >> >> I'm a new user of Persuite/PAPI and would appreciate comments >> on my query below. >> >> On a quad core intel runing Fedora Core 6 (kernel 2.6.18), I >> get the following numbers while runing a *single* threaded >> program: >> CPU time (seconds) 47.966 >> Wall clock time (seconds) 30.582 >> >> Since the CPU time > Wall clock time, one conclusion might me >> a bug in Perfsuite/PAPI or somewhere else. I double checked >> the CPU >> time by dividing PAPI_TOT_CYC count by CPU frequency, and I >> arrive at the same number. Any ideas on what might be going on >> or what might be the best approach to debugging this problem >> is appreciated. >> >> Thanks, >> -Naveen >> >> ------------------------------------------------------------------------ >> >> >> ------------------------------------------------------------------------------ >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> PerfSuite-users mailing list >> Per...@li... >> <mailto:Per...@li...> >> https://lists.sourceforge.net/lists/listinfo/perfsuite-users >> >> >> >> > |
