On 04/24/2014 10:19 AM, Hidetoshi Seto wrote: > As I already mentioned in previous discussion with Peter, I have > concern here that this change might have impact on performance. > Especially in case if system is a kind of io-busy box, originally > there may be no iowait time (and possibly also no idle time). > For such case this change adds extra execution cost to manage > value of iowait_exittime which might not used.
Everything has some cost. Correctness usually trumps a few extra locked bus cycles. Wouldn't it be nice if we'd know whether anyone even needs the stats? If no one going to read /proc/stat on the box, there's no point in going to all the trouble to maintain the counters... > And if we successfully found a way to get the iowait_exittime > within reasonable negligible cheap cost, then why we don't use > it for NOHZ=n kernels too? Kernels without NOHZ maintain the counters based on timer interrupt sampling. It should still work fine. > As Frederic already pointed, seqcount must be better choice. Yes, I'm switching to seqcounts. -- 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/
