linux-kernel - Re: [RFC] resource: Avoid unnecessary resource tree walking in __region

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Message-ID: <b8262026-533b-497b-9713-fa3e32f76d9f@redhat.com>
Date: Fri, 11 Oct 2024 12:51:09 +0200
From: David Hildenbrand <david@...hat.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 "Huang, Ying" <ying.huang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, linux-cxl@...r.kernel.org,
 Dan Williams <dan.j.williams@...el.com>, Davidlohr Bueso
 <dave@...olabs.net>, Jonathan Cameron <jonathan.cameron@...wei.com>,
 Alistair Popple <apopple@...dia.com>, Bjorn Helgaas <bhelgaas@...gle.com>,
 Baoquan He <bhe@...hat.com>, Dave Jiang <dave.jiang@...el.com>,
 Alison Schofield <alison.schofield@...el.com>
Subject: Re: [RFC] resource: Avoid unnecessary resource tree walking in
 __region_intersects()

On 11.10.24 12:49, Andy Shevchenko wrote:
> On Fri, Oct 11, 2024 at 09:06:37AM +0800, Huang, Ying wrote:
>> David Hildenbrand <david@...hat.com> writes:
>>> On 10.10.24 08:55, Huang Ying wrote:
> 
> ...
> 
>>> 	for ((_p) = (_root)->child; (_p); (_p) = next_resource_XXX(_root, _p))
>>
>> Yes.  This can improve code readability.
>>
>> A possible issue is that "_root" will be evaluated twice in above macro
>> definition.  IMO, this should be avoided.
> 
> Ideally, yes. But how many for_each type of macros you see that really try hard
> to achieve that? I believe we shouldn't worry right now about this and rely on
> the fact that root is the given variable. Or do you have an example of what you
> suggested in the other reply, i.e. where it's an evaluation of the heavy call?
> 
>> Do you have some idea about
>> how to do that?  Something like below?
>>
>> #define for_each_resource_XXX(_root, _p)                                \
>> 	for (typeof(_root) __root = (_root), __p = (_p) = (__root)->child; \
>> 	     __p && (_p); (_p) = next_resource_XXX(__root, _p))
> 
> This is a bit ugly :-( I would avoid ugliness as long as we have no problem to
> solve (see above).

Fully agreed, I didn't quite understand the concern about "evaluation" 
at first. If it's just reading a variable twice, it doesn't matter at 
all right now.

-- 
Cheers,

David / dhildenb