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    SubjectRe: [PATCH v3 01/18] Documentation, ABI: Add a document entry for cache id
    On Sat, Oct 08, 2016 at 12:11:08PM -0500, Nilay Vaish wrote:
    > On 7 October 2016 at 21:45, Fenghua Yu <fenghua.yu@intel.com> wrote:
    > > From: Fenghua Yu <fenghua.yu@intel.com>

    > > + caches typically exist per core, but there may not be a
    > > + power of two cores on a socket, so these caches may be
    > > + numbered 0, 1, 2, 3, 4, 5, 8, 9, 10, ...
    > > +
    >
    > While it is ok that the caches are not numbered contiguously, it is
    > unclear how this is related to number of cores on a socket being a
    > power of 2 or not.

    That's a side effect of the x86 algorithm to generate the unique ID
    which uses a shift to put the socket number in some upper bits while
    leaving the "id within a socket" in the low bits.

    I don't think it worth documenting here, but I noticed that we don't
    keep the IDs within a core contguous either. On my 24 core Broadwell
    they are not 0 ... 23 then a gap from 24 to 31. I actually have on
    socket 0:

    0, 1, 2, 3, 4, 5
    8, 9, 10, 11, 12, 13
    16, 17, 18, 19, 20, 21
    24, 25, 26, 27, 28, 29

    -Tony

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