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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

~Andrew