Re: [Qemu-block] [Qemu-devel] [PATCH v2 1/2] block/accounting: introduce latency histogram

[Vladimir Sementsov-Ogievskiy]

08.03.2018 21:14, Vladimir Sementsov-Ogievskiy wrote:
> 08.03.2018 20:31, Eric Blake wrote:
> > On 03/06/2018 09:32 AM, Stefan Hajnoczi wrote:
> > > On Wed, Feb 07, 2018 at 03:50:36PM +0300, Vladimir 
> > > Sementsov-Ogievskiy wrote:
> > > > Introduce latency histogram statics for block devices.
> > > > For each accounted operation type latency region [0, +inf) is
> > > > divided into subregions by several points. Then, calculate
> > > > hits for each subregion.
> > > >
> > > > Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
> > > > ---
> >
> > > According to Wikipedia and Mathworld, "intervals" and "bins" are
> > > commonly used terms:
> > > https://en.wikipedia.org/wiki/Histogram
> > > http://mathworld.wolfram.com/Histogram.html
> > >
> > > I suggest:
> > >
> > >    typedef struct {
> > >        /* The following histogram is represented like this:
> > >         *
> > >         * 5|           *
> > >         * 4|           *
> > >         * 3| *         *
> > >         * 2| *         *    *
> > >         * 1| *    *    *    *
> > >         *  +------------------
> > >         *      10   50   100
> > >         *
> > >         * BlockLatencyHistogram histogram = {
> > >         *     .nbins = 4,
> > >         *     .intervals = {10, 50, 100},
> > >         *     .bins = {3, 1, 5, 2},
> > >         * };
> >
> > The name 'intervals' is still slightly ambiguous: does it hold the 
> > boundary point (0-10 for 10 slots, 10-50 for 40 slots, 50-100, for 50 
> > slots, then 100-INF) or is it the interval size of each slot (first 
> > bin is 10 slots for 0-10, next bin is 50 slots wide so 10-60, next 
> > bin is 100 slots wide so 60-160, everything else is 160-INF).  But 
> > the ascii-art diagram plus the text is sufficient to resolve the 
> > intent if you keep that name (I don't have a suggestion for a better 
> > name).
>
> Hm. these numbers are actually boundary points of histogram intervals, 
> not intervals itself. And, wiki says "The bins are usually specified 
> as consecutive, non-overlapping intervals of a variable.", so, 
> intervals are bins.
>
> So, what about:
>
> 1. interval_boundaries
> 2. bin_boundaries
> 3. boundaries
>
> (and same names with s/_/-/ for qapi)


Also, now I doubt, is it a good idea to share same bin boundaries for 
each io type.

--
Best regards,
Vladimir