Subject: Re: [PATCH v2] powerpc: kernel: remove useless code which related with 'max_cpus'

From: Chen Gang <[email-masked]>
Date: Thu, 25 Jul 2013 12:02:54 +0800

On 07/25/2013 11:15 AM, Michael Ellerman wrote:
> On Wed, Jul 24, 2013 at 10:09:33AM +0800, Chen Gang wrote:
>> > On 07/24/2013 09:16 AM, Michael Ellerman wrote:
>>> > > On Wed, Jul 24, 2013 at 08:28:07AM +0800, Chen Gang wrote:
>>>>> > >> > On 07/23/2013 09:44 PM, Michael Ellerman wrote:
>>>>>>> > >>> > > On Mon, Jul 22, 2013 at 12:21:16PM +0530, Srivatsa S. Bhat wrote:
>>>>>>>>> > >>>> > >> On 07/22/2013 12:10 PM, Chen Gang wrote:
>>>>>>>>>>> > >>>>> > >>> Since not need 'max_cpus' after the related commit, the related code
>>>>>>>>>>> > >>>>> > >>> are useless too, need be removed.
>>>>>>> > >>> > > 
>>>>>>> > >>> > > A good follow up patch, or actually series of patches, would be to
>>>>>>> > >>> > > change the prototype of smp_ops->probe() to return void, and fix all the
>>>>>>> > >>> > > implementations to no longer return anything.
>>>>>>> > >>> > > 
>>>>> > >> > 
>>>>> > >> > Hmm... normally, a function need have a return value, it will make it
>>>>> > >> > more extensible (especially, it is an API which need be implemented in
>>>>> > >> > various sub modules).
>>> > > A function doesn't need a return value, and if it needs one in future then
>>> > > we'll add it then. We don't carry code around "just in case".
>> > 
>> > But for API (also include the internal API), at least, better to always
>> > provide the return value which can indicate failure by negative number
>> > (if succeed can return the meanness value, e.g. the number of cpus).
> Are we still talking about this?
> 
> There is no point returning a value when no one checks it. Which is the
> case here.
> 
> For a published API maybe it's a good idea to have a return value "just
> in case", but this is kernel internal and we own both the implementation
> and the callers of the API.
> 

API is between caller and callee, but independent with who will use it
and who will implement it (may be they are the same member), and also
independent with whether "between kernel and user" or not.

Today, you are really the member for both caller and callee, but in the
future, may not.

For our case, it is really an API, it is defined in upper level, and
implement in various sub modules (extern the declaration and implement
in various sub modules).

>>>>> > >> > Even though the return value may be useless, now, if the performance is
>>>>> > >> > not quite important in our case, I still suggest to have it (especially
>>>>> > >> > each various original implementation already has it).
>>> > > It's dead code, it should be removed.
>> > 
>> > For API, if not cause the real world issue, better to keep compatible
>> > (especially, the return value still can indicate failure by negative
>> > number).
> No. Dead code is a real world issue. If we ever need a return value
> we'll add one then.

Hmm... what my original saying "real world issue" is not precise, it
need change to: "if it is not an 'urgent' issue (may be a real world
issue), for API, need still keep it compatible (keep no touch) now".

"dead code for an API" does not belong to 'urgent' issue, it belongs to
'important' issue.  When we are reconstructing the source code, we can
also remove them in that window (at least, it does not often happen).

(although for our case, I don't think "return value for API" is "dead
code for an API")

Thanks.
-- 
Chen Gang