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Message-ID: <4A09FD81.8090805@linux.vnet.ibm.com> Date: Tue, 12 May 2009 15:51:45 -0700 From: Corey Ashford <cjashfor@...ux.vnet.ibm.com> To: Paul Mackerras <paulus@...ba.org> CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de> Subject: Re: [PATCH 3/5] perf_counter: rework ioctl()s Paul Mackerras wrote: > Corey Ashford writes: > >> Another hypothesis is that the old PAPI code would open, mmap, close, >> then reopen, and mmap again. I wonder if because I wasn't munmap'ing >> before the close, that I got some strange behavior from the kernel. > > In general an mmap will keep a reference to the file it is mapping, > which means that if you do an mmap on a fd and then close the fd, the > file stays open until the region is munmapped. So your old PAPI code > would have ended up with more counters active than you expected, if > you thought closing the fd would have destroyed the counter. > > That is, you don't have to munmap before close, but you do have to do > both close and munmap to destroy the counter. That makes perfect sense. I'll bet that's what the problem was. I think this issue can be closed. Thank you Paul M. and Peter Z. for looking into this. - Corey -- 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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