On Thu, Sep 01, 2022 at 12:00:17AM +0800, Coly Li wrote: > > > > 2022年8月30日 00:53，Kent Overstreet <kent.overstreet@xxxxxxxxx> 写道： > > > > This patch converts bcache to the new generic time_stats code > > lib/time_stats.c. The new code is from bcachefs, and has some changes > > from the version in bcache: > > > > - we now use ktime_get_ns(), not local_clock(). When the code was > > originally written multi processor systems that lacked synchronized > > TSCs were still common, and so local_clock() was much cheaper than > > sched_clock() (though not necessarily fully accurate, due to TSC > > drift). ktime_get_ns() should be cheap enough on all common hardware > > now, and more standard/correct. > > > > - time_stats are now exported in a single file in sysfs, which means we > > can improve the statistics we keep track of without changing all > > users. This also means we don't have to manually specify which units > > (ms, us, ns) a given time_stats should be printed in; that's handled > > dynamically. > > > > - There's a lazily-allocated percpu buffer, which now needs to be freed > > with time_stats_exit(). > > > > Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> > > Cc: Coly Li <colyli@xxxxxxx> > > Hi Kent, > > Overall I am OK with the change to bcache code. You may add > Acked-by: Coly Li <colyli@xxxxxxx> > in future version of this patch. > > In bcache-tools, they don’t read the changed sysfs files (including bcache-status), IMHO changing the output format won’t be problem for upstream. > > My only question is, how to understand the time_stats_to_text() output format, > count: 3 > rate: 0/sec > frequency: 4 sec > avg duration: 4 sec > max duration: 4 sec > quantiles (ns): 0 4288669120 4288669120 5360836048 5360836048 5360836048 5360836048 5360836048 5360836048 5360836048 5360836048 5360836048 5360836048 5360836048 5360836048 > > Fro the above output, what are “rate”, “frequence” and “quantiles” for? Rate and frequency are inverses - in this example, we're seeing 4 events per second. The quantiles are for the duration, they give you an idea of the statistical distribution, see https://en.wikipedia.org/wiki/Quantile In the near future, the quantiles will be removed and replaced with standard deviation, true and weighted - the quantiles algorithm isn't super accurate, we can give more accurate numbers with standard deviation.
