Looks Good. Thanks for your improvement. Reviewed-by Guan Junxiong <guanjunxiong@xxxxxxxxxx> On 2018/1/14 5:19, Martin Wilck wrote: > The warnings at here are pointless. We are looking at a single > path only. Firstly, the standdard deviation for this measurement > can't be "too low" - the lower, the more precise the measurement, > the better. Secondly, a high standard deviation indicates an > unstable path with highly variable latency. Not good, but nothing > to warn about here. > > What matters for the selection of "base_num" is not how a single > path behaves, but how different paths of the same path group relate > to each other, which we don't know at this point at the code. > > What we want to avoid is too fine a differentiation, in particular > in combination with group_by_prio, because we'd loose the ability for > load balancing. But this is rather a topic for the man page or a > "best practices" document. > --- > libmultipath/prioritizers/path_latency.c | 34 -------------------------------- > 1 file changed, 34 deletions(-) > > diff --git a/libmultipath/prioritizers/path_latency.c b/libmultipath/prioritizers/path_latency.c > index e764f1dd8a21..765265c02333 100644 > --- a/libmultipath/prioritizers/path_latency.c > +++ b/libmultipath/prioritizers/path_latency.c > @@ -289,40 +289,6 @@ int getprio(struct path *pp, char *args, unsigned int timeout) > return DEFAULT_PRIORITY; > } > > - standard_deviation = calc_standard_deviation(lg_path_latency, > - index, lg_avglatency); > - /* > - * In calPrio(), we let prio y = f(x) = log(max, base) - log (x, base); > - * So if we want to let the priority of the latency outside 2 standard > - * deviations can be distinguished from the latency inside 2 standard > - * deviation, in others words at most 95% are the same and at least 5% > - * are different according interval estimation of normal distribution, > - * we should warn the user to set the base_num to be smaller if the > - * log(x_threshold, base) is small than 2 standard deviation. > - * x_threshold is derived from: > - * y + 1 = f(x) + 1 = f(x) + log(base, base), so x_threadshold = > - * base_num; Note that we only can compare the logarithm of x_threshold > - * with the standard deviation because the standard deviation is derived > - * from logarithm of latency. > - * > - * therefore , we recommend the base_num to meet the condition : > - * 1 <= 2 * standard_deviation > - */ > - pp_pl_log(5, "%s: standard deviation for logarithm of latency = %.6f", > - pp->dev, standard_deviation); > - if (standard_deviation <= 0.5) > - pp_pl_log(3, "%s: the base_num(%.3lf) is too big to distinguish different priority " > - "of two far-away latency. It is recommend to be set smaller", > - pp->dev, base_num); > - /* > - * If the standard deviation is too large , we should also warn the user > - */ > - > - if (standard_deviation > 4) > - pp_pl_log(3, "%s: the base_num(%.3lf) is too small to avoid noise disturbance " > - ".It is recommend to be set larger", > - pp->dev, base_num); > - > standard_deviation = sqrt((sum_squares - lg_toldelay * lg_avglatency) > / (io_num - 1)); > > -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
