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


  • To: George Dunlap <george.dunlap@xxxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Wed, 20 Mar 2024 12:19:36 +0000
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Dario Faggioli <dfaggioli@xxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>, "consulting @ bugseng . com" <consulting@xxxxxxxxxxx>
  • Delivery-date: Wed, 20 Mar 2024 12:19:45 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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.

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

~Andrew



 


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