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

["Oleksii K." <oleksii.kurochko@xxxxxxxxx>]

On Tue, 2024-05-14 at 14:52 +0100, Andrew Cooper wrote:
> On 14/05/2024 1:36 pm, Leigh Brown wrote:
> > Hello,
> > 
> > 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?
> > 
> > Without patch:
> > 
> > xentop - 13:29:01   Xen 4.18.2
> > 13 domains: 1 running, 12 blocked, 0 paused, 0 crashed, 0 dying, 0
> > shutdown
> > Mem: 67030640k total, 33097800k used, 33932840k free    CPUs: 24 @
> > 3693MHz
> >       NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)  MAXMEM(k)
> > MAXMEM(%)
> >   icecream --b---       2597    6.6    4194368    6.3   
> > 4195328       6.3
> >      xendd --b---       4016    5.4     524268    0.8    
> > 525312       0.8
> >   Domain-0 -----r       1059    1.7    1048576    1.6   
> > 1048576       1.6
> >       neon --b---        826    1.1    2097216    3.1   
> > 2098176       3.1
> >    blender --b---        121    0.2    1048640    1.6   
> > 1049600       1.6
> >      bread --b---         69    0.1     524352    0.8    
> > 525312       0.8
> >        bob --b---        502    0.3   16777284   25.0  
> > 16778240      25.0
> >     cheese --b---        225    0.5    1048384    1.6   
> > 1049600       1.6
> >    cassini --b---        489    0.4    3145792    4.7   
> > 3146752       4.7
> >   chickpea --b---         67    0.1     524352    0.8    
> > 525312       0.8
> >     lentil --b---         67    0.1     262208    0.4    
> > 263168       0.4
> >    fusilli --b---        159    0.2     524352    0.8    
> > 525312       0.8
> >      pizza --b---        359    0.5     524352    0.8    
> > 525312       0.8
> > 
> > With patch:
> > 
> > xentop - 13:30:17   Xen 4.18.2
> > 13 domains: 1 running, 12 blocked, 0 paused, 0 crashed, 0 dying, 0
> > shutdown
> > Mem: 67030640k total, 33097788k used, 33932852k free    CPUs: 24 @
> > 3693MHz
> >       NAME  STATE   CPU(sec) CPU(%)     MEM(k) MEM(%)  MAXMEM(k)
> > MAXMEM(%)
> >      xendd --b---       4020    5.7     524268    0.8    
> > 525312       0.8
> >   icecream --b---       2600    3.8    4194368    6.3   
> > 4195328       6.3
> >   Domain-0 -----r       1060    1.5    1048576    1.6   
> > 1048576       1.6
> >       neon --b---        827    1.1    2097216    3.1   
> > 2098176       3.1
> >     cheese --b---        225    0.7    1048384    1.6   
> > 1049600       1.6
> >      pizza --b---        359    0.5     524352    0.8    
> > 525312       0.8
> >    cassini --b---        490    0.4    3145792    4.7   
> > 3146752       4.7
> >    fusilli --b---        159    0.2     524352    0.8    
> > 525312       0.8
> >        bob --b---        502    0.2   16777284   25.0  
> > 16778240      25.0
> >    blender --b---        121    0.2    1048640    1.6   
> > 1049600       1.6
> >      bread --b---         69    0.1     524352    0.8    
> > 525312       0.8
> >   chickpea --b---         67    0.1     524352    0.8    
> > 525312       0.8
> >     lentil --b---         67    0.1     262208    0.4    
> > 263168       0.4
> 
> 
> Ah, so it's the rounding, and a straight cast discards the fractional
> part.
> 
> I think your patch is fine, although it could do with a mention of
> why
> this goes wrong in the commit message.  I'm happy to adjust on
> commit.
Feel free to merge it as I am considering it as bugfix:
 Release-acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

~ Oleksii
> 
> ~Andrew