On Tue, Apr 03, 2007 at 10:59:53AM -0700, Ulrich Drepper wrote: > Siddha, Suresh B wrote: > > Not all of the cpu* directories in /sys/devices/system/cpu may be > > online. > > Brilliant. You people really know how to create user interfaces. So > now in any case per CPU another stat/access syscall is needed to check > the 'online' pseudo-file? With this the readdir solution is only > marginally faster than parsing /proc/cpuinfo which means, it's > unacceptably slow.
Note that glibc actually parses /proc/stat in preference of /proc/cpuinfo ATM, because /proc/stat is at least uniform while parsing /proc/cpuinfo needs a special parser for each architecture. And /proc/stat reading is even slower than /proc/cpuinfo, on x86_64 reading/parsing /proc/stat takes about 450usec, while e.g. stat64 on /sys/devices/system/cpu is just 2.5usec. But if that can't be trusted as the number of online CPUs, can somebody please add a short file to proc or sysfs which will contain the number of online and number of configured CPUs? See e.g. http://openmp.org/pipermail/omp/2007/000714.html where the first time after second g++ invocation is with omp_set_dynamic (1) and ought to be about as fast as omp_set_dynamic (0) case with the same number of threads, but it is far slower due to slow sysconf (_SC_NPROCESSORS_ONLN). Jakub - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
