On Mon, Jan 30, 2006 at 06:54:29PM +0000, Philip Mucci wrote: > In reference to the performance counting thread we had going earlier, > I've noticed a 'feature' I need out of MIPS/Linux that isn't currently > available. This has also recently come up on the oprofile list with one > of the oprofile/mips tools not being able to grab cpu Mhz > from /proc/cpuinfo because it's not there. Surprise - the kernel doesn't actually have that information. The closest available would be the counting speed of the c0 count register which - if something like that is available at all - could be calibrated against an external counter to figure out the clock speed. To complicate matters not all processors have have a c0 counter, it's sometimes incrementing every cycle but it might just as well counting at half the clock rate and oh yes, more recently there is clock scaling. > I have need to execute the mfc0 instruction on the config register and > grok the results to find out things like cache size etc. In addition, it > might be nice to also actually be able to find out the clock rate. > (Currently I grab BogoMIPS and punt.) Considering above complexities a BogoMIPS-based approach doesn't sound too bad - but it has other problem to implement since it requires knowing the exact execution timing. A think that could be done is meassuring two loops containing a different number of nops and use that to compute the execution time for the loop closing branch. Now knowing that based on knowing the # of cycles per loop we can compute the clock speed - all it takes is a timer running at a known speed. A funny complexity is that some multiprocessor MIPS systems have processors running at different speeds. So knowing the clock rate doesn't make life too much easier ;-) > On the intel and PPC systems, I believe you can execute similar > instructions from user mode which makes things easy. However, of course > an MFC0 is a privileged instruction...meaning that if the value or > values aren't found in /proc/cpuinfo, I'm s.o.l. We have a long tradition of emulating instructions, could use that to permit access to a bunch of cp0 registers from userland ;) > What does the list think about this? Making a mips /dev/cpuid is a bit > gross but extending and grokking /proc/cpuinfo is perhaps grosser...and > many tools do just this (like PAPI and oprofile's opreport...) > > Comments? I'm certainly willing to implement this, but I'd rather 'do it > right the first time' rather than get rotten vegetables thrown my way. /proc/cpuinfo is meant to have per processor information so I don't have a problem with adding cache configuration information. I was considering to do so to make such information available for bug reports. Ralf
