linux-kernel - Re: [PATCH 01/11] resource: Add System RAM resource type

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Message-ID: <20151216181712.GJ29775@pd.tnic>
Date:	Wed, 16 Dec 2015 19:17:12 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Toshi Kani <toshi.kani@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org, Linux MM <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 01/11] resource: Add System RAM resource type

On Wed, Dec 16, 2015 at 09:52:37AM -0800, Dan Williams wrote:
> It's possible that as far as the resource table is concerned the
> resource type might just be "reserved".  It may not be until after a
> driver loads that we discover the memory range type.  The identifying
> string is driver specific at that point.

So how many types are we talking about here? Because I don't find a whole lot:

$ git grep -E "(walk_iomem_res|find_next_iomem_res|region_intersects)" -- *.c | grep -Eo '\".*\"'
"GART"
"ACPI Tables"
"ACPI Non-volatile Storage"
"Crash kernel"
"System RAM"
"System RAM"
"System RAM"

An int type could contain 2^32 different types.

> All this to say that with strcmp we can search for any custom type .
> Otherwise I think we're looking at updating the request_region()
> interface to take a type parameter.  That makes strcmp capability more
> attractive compared to updating a potentially large number of
> request_region() call sites.

Right, but I don't think that @name param to request_region() was ever
meant to be mis-used as a matching attribute when iterating over the
resource types.

Now, imagine you have to do this pretty often. Which is faster: a
strcmp() or an int comparison...?

Even if this cannot be changed easily/in one go, maybe we should at
least think about starting doing it right so that the strcmp() "fun" is
phased out gradually...

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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