On 03/24/2014 01:51 PM, Hidetoshi Seto wrote: > (2014/03/24 16:45), Preeti Murthy wrote: >> Hi Hidetoshi, >> >> The patch looks good to me except the comments around the monotonicity >> of the return value of the idle stats observer. I am unable to relate them >> to the dependency on nr_iowait_cpu. >> >> I see that when the reader queries for the idle stats and calls >> get_cpu_idle_time_us(), the nr_iowait_cpu might be 0. When he later >> queries get_cpu_iowait_time_us(), it may be >0 . Hence we will be >> accounting for the idle time in both idle time and iowait time. This >> is definitely a problem. But I do not understand what this has got to >> do with the monotonicity of the time >> returned. This is just for my understanding. > > Thank you for your comment! > > Ah yes, I think I could write better comments around here to clarify > the monotonicity problem. (It will be happy if someone can give me > such better sentence for here :-D) > > One important point is that readers do not update idle stats when they > use these function. i.e. > > given: > idle stats: idle=1000, iowait=100 > stamp at idle entry: entry=50 > nr tasks waiting io: nr_iowait=1 > > 1st reader: > query @ now=60 > idle=1000 > iowait=110 (=100+(60-50)) > > (here nr_iowait changed to 0) > > 2nd reader: > query @ now=70 > idle=1020 (=1000+(70-50)) > iowait=100 > > So you will see iowait is decreased from 110 to 100.
Ah ok! I get it. Please do add my Reviewed-by to it. > > I hope this short story helps you. Thanks! Regards Preeti U Murthy > > Thanks, > H.Seto > -- 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/
