Messages in this thread | | | From | "Julio M. Merino Vidal" <> | Subject | Per-CPU data as a structure | Date | Thu, 3 May 2007 17:16:17 +0200 |
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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@ac.upc.edu>
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