On Mon, Oct 07, 2013 at 06:09:15PM +0200, Stephane Eranian wrote: > The counters all count in the same unit. The perf_events API > exposes all RAPL counters as 64-bit integers counting in unit > of 1/2^32 Joules (or 0.23 nJ). User level tools must convert > the counts by multiplying them by 0.23 and divide 10^9 to > obtain Joules. The reason for this is that the kernel avoids > doing floating point math whenever possible because it is > expensive (user floating-point state must be saved). The method > used avoids kernel floating-point and minimizes the loss of > precision (bits). Thanks to PeterZ for suggesting this approach. > > To convert the raw count in Watt: W = C * 0.23 / (1e9 * time)
Right, so the output is in 32.32 fixed point. So if you want to convert to double you'd do something like: double watt = ldexp(counter, -32); -- 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/
