Re: [PATCH for-4.19] tools/xentop: fix cpu% sort order

[Leigh Brown <leigh@xxxxxxxxxxxxx>]

On 2024-05-14 13:07, Andrew Cooper wrote:
> On 14/05/2024 9:13 am, Leigh Brown wrote:
> > Although using integer comparison to compare doubles kind of
> > works, it's annoying to see domains slightly out of order when
> > sorting by cpu%.
> >
> > Add a compare_dbl() function and update compare_cpu_pct() to
> > call it.
> >
> > Signed-off-by: Leigh Brown <leigh@xxxxxxxxxxxxx>
> > ---
> >  tools/xentop/xentop.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/xentop/xentop.c b/tools/xentop/xentop.c
> > index 545bd5e96d..99199caec9 100644
> > --- a/tools/xentop/xentop.c
> > +++ b/tools/xentop/xentop.c
> > @@ -85,6 +85,7 @@ static void set_delay(const char *value);
> >  static void set_prompt(const char *new_prompt, void (*func)(const 
> > char *));
> >  static int handle_key(int);
> >  static int compare(unsigned long long, unsigned long long);
> > +static int compare_dbl(double, double);
> >  static int compare_domains(xenstat_domain **, xenstat_domain **);
> >  static unsigned long long tot_net_bytes( xenstat_domain *, int);
> >  static bool tot_vbd_reqs(xenstat_domain *, int, unsigned long long 
> > *);
> > @@ -422,6 +423,16 @@ static int compare(unsigned long long i1, 
> > unsigned long long i2)
> >         return 0;
> >  }
> >
> > +/* Compares two double precision numbers, returning -1,0,1 for <,=,> 
> > */
> > +static int compare_dbl(double d1, double d2)
> > +{
> > +       if(d1 < d2)
> > +               return -1;
> > +       if(d1 > d2)
> > +               return 1;
> > +       return 0;
> > +}
> > +
> >  /* Comparison function for use with qsort.  Compares two domains 
> > using the
> >   * current sort field. */
> >  static int compare_domains(xenstat_domain **domain1, xenstat_domain 
> > **domain2)
> > @@ -523,7 +534,7 @@ static double get_cpu_pct(xenstat_domain *domain)
> >
> >  static int compare_cpu_pct(xenstat_domain *domain1, xenstat_domain 
> > *domain2)
> >  {
> > -       return -compare(get_cpu_pct(domain1), get_cpu_pct(domain2));
> > +       return -compare_dbl(get_cpu_pct(domain1), get_cpu_pct(domain2));
> Oh, we were doing an implicit double->unsigned long long conversion. 
> Over the range 0.0 to 100.0, that ought to work as expected.  What kind
> of out-of-order are you seeing?
>
> Nevertheless, this should comparison should clearly be done using
> doubles.  AFACT, get_cpu_pct() shouldn't ever return a NaN, so I think
> this simple form is fine.
>
> Oleksii: This is another bugfix to xentop, and should be considered for
> 4.19 at this point.
>
> ~Andrew
Perhaps I overthought it, and this approach might be better:

--- a/tools/xentop/xentop.c
+++ b/tools/xentop/xentop.c
@@ -523,7 +523,8 @@ static double get_cpu_pct(xenstat_domain *domain)

 static int compare_cpu_pct(xenstat_domain *domain1, xenstat_domain 
*domain2)
 {
-       return -compare(get_cpu_pct(domain1), get_cpu_pct(domain2));
+       return -compare(get_cpu_pct(domain1) * 100.0,
+                       get_cpu_pct(domain2) * 100.0);
 }

 /* Prints cpu percentage statistic */