lkml.org 
[lkml]   [2007]   [May]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    SubjectPer-CPU data as a structure
    Date
    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>


    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-05-03 17:51    [W:0.037 / U:94.912 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site