[<prev] [next>] [thread-next>] [day] [month] [year] [list]
Message-Id: <16C35E62-A26F-49FC-9CD8-7BADFCD97BA5@ac.upc.edu>
Date: Thu, 3 May 2007 17:16:17 +0200
From: "Julio M. Merino Vidal" <jmerino@...upc.edu>
To: linux-kernel@...r.kernel.org
Subject: Per-CPU data as a structure
Hello,
At the moment, data specific to a CPU is stored in different, fixed-
size separate arrays by means of the "percpu framework". I'm working
on some changes to modify the way some CPUs are represented, and I'm
wondering what's the rationale behind such a representation.
At first sight, it'd seem more reasonable to have a structure holding
all the information that is CPU-specific (as is done with any object
represented within the system). After searching the mail archives, I
see that similar changes were proposed before, but those threads did
not seem to get any reply (so I'm assuming that the changes were not
desired).
Similarly, and if I understood it correctly, the PDA (Per-processor
Data Area) also aims to do the above, but at the moment it only
contains some fields and is not defined in all platforms. There are
still a lot of usages of the percpu functionality (such as, e.g., in
kernel/sched.c).
Part of my changes introduce a new structure that is able to
represent any kind of CPU (and which each platform can extend to add
new information to it). It is supposed to supersede the per-cpu
definitions. I bet this could also be redone by using percpu in some
way... The thing is I am willing to share my work when I've finished
it (it is still very much work-in-progress), but first I'm interested
to know if adding this new structure is a crazy idea (meaning I
should stick to percpu wherever possible) or something that can be
accepted later on.
Summarizing, my questions are:
- Why is the code currently using multiple separate arrays (percpu)
to hold CPU information instead of a structure?
- Could this structure-based approach (instead of all these separate
arrays) be considered for inclusion into the system?
As far as I can tell, the advantage of percpu is that you can define
new "fields" anywhere in the code and independently from the rest of
the system. Also, I seem to understand that there are performance
advantages related to this. But on the other hand, percpu seems like
an unnatural approach to "reimplement" regular structures.
Thank you very much.
--
Julio M. Merino Vidal <jmerino@...upc.edu>
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists