Re: [PATCH 2/7] xen/credit2: Clean up trace handling

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.03.2024 13:19, Andrew Cooper wrote:
> On 20/03/2024 12:16 pm, George Dunlap wrote:
>> On Mon, Mar 18, 2024 at 4:36 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 
>> wrote:
>>> There is no need for bitfields anywhere - use more sensible types.  There is
>>> also no need to cast 'd' to (unsigned char *) before passing it to a 
>>> function
>>> taking void *.  Switch to new trace_time() API.
>>>
>>> No functional change.
>> Hey Andrew -- overall changes look great, thanks for doing this very
>> detailed work.
>>
>> One issue here is that you've changed a number of signed values to
>> unsigned values; for example:
>>
>>> @@ -1563,16 +1559,16 @@ static s_time_t tickle_score(const struct scheduler 
>>> *ops, s_time_t now,
>>>      if ( unlikely(tb_init_done) )
>>>      {
>>>          struct {
>>> -            unsigned unit:16, dom:16;
>>> -            int credit, score;
>>> -        } d;
>>> -        d.dom = cur->unit->domain->domain_id;
>>> -        d.unit = cur->unit->unit_id;
>>> -        d.credit = cur->credit;
>>> -        d.score = score;
>>> -        __trace_var(TRC_CSCHED2_TICKLE_CHECK, 1,
>>> -                    sizeof(d),
>>> -                    (unsigned char *)&d);
>>> +            uint16_t unit, dom;
>>> +            uint32_t credit, score;
>> ...here you change `int` to `unit32_t`; but `credit` and `score` are
>> both signed values, which may be negative.  There are a number of
>> other similar instances.  In general, if there's a signed value, it
>> was meant.
> 
> Oh - this is a consequence of being reviewed that way in earlier iterations.

Which in turn is a result of us still having way to many uses of plain
int when signed quantities aren't meant. Plus my suggestion to make
this explicit by saying "signed int" was rejected.

> If they really can hold negative numbers, they can become int32_t's. 
> What's important is that they have a clearly-specified width.

And please feel free to retain my R-b with any such adjustments.

Jan