Vince Weaver writes: > On Fri, 30 Aug 2013, Stephane Eranian wrote: > > > > > You mean that the high cost in your first example comes from the fact > > that you are averaging over all the iterations and not n-1 (where 1 is > > the first). I don't see a flag in mmap() to fault it in immediately. But > > why not document, that programs should touch the page once before > > starting any timing measurements. > > I was just curious why perfctr didn't need to do this, but possibly > I'm just missing the mmap page being touched. Though the code is pretty > small and I'm not seeing any such access.
perfctr's ->mmap() actively inserts the counters page into the calling process' mm, so it's available immediately. The other model is to wait for the first page fault on that page before inserting it; apparently the other performance counter frameworks do that instead. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
