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    SubjectRe: [PATCH v4 5/5] sched: ARM: create a dedicated scheduler topology table
    On 24 April 2014 14:48, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
    > On 24/04/14 08:30, Vincent Guittot wrote:
    >> On 23 April 2014 17:26, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
    >>> On 23/04/14 15:46, Vincent Guittot wrote:
    >>>> On 23 April 2014 13:46, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
    >>>>> Hi,
    >
    > [...]
    >
    >>
    >> More than the flag that is used for the example, it's about the
    >> cpumask which are inconsistent across CPUs for the same level and the
    >> build_sched_domain sequence rely on this consistency to build
    >> sched_group
    >
    > Now I'm lost here. I thought so far that by specifying different cpu
    > masks per CPU in an sd level, we get the sd level folding functionality
    > in sd degenerate?
    >
    > We discussed this here for an example on TC2 for the GMC level:
    > https://lkml.org/lkml/2014/3/21/126
    >
    > Back than I had
    > CPU0: cpu_corepower_mask=0-1
    > CPU2: cpu_corepower_mask=2
    > so for GMC level the cpumasks are inconsistent across CPUs and it worked.

    The example above is consistent because CPU2 mask and CPU0 mask are
    fully exclusive

    so
    CPU0: cpu_corepower_mask=0-1
    CPU2: cpu_corepower_mask=2
    are consistent

    CPU0: cpu_corepower_mask=0-2
    CPU2: cpu_corepower_mask=0-2
    are also consistent

    but

    CPU0: cpu_corepower_mask=0-1
    CPU2: cpu_corepower_mask=0-2
    are not consistent

    and your example uses the last configuration

    To be more precise, the rule above applies on default SDT definition
    but the flag SD_OVERLAP enables such kind of overlap between group.
    Have you tried it ?

    Vincent

    >
    > The header of '[PATCH v4 1/5] sched: rework of sched_domain topology
    > definition' mentions only the requirement "Then, each level must be a
    > subset on the next one" and this one I haven't broken w/ my
    > GMC/MC/GDIE/DIE set-up.
    >
    > Do I miss something else here?
    >
    >>
    >>> Essentially what I want to do is bind an SD_SHARE_*FOO* flag to the GDIE
    >>> related sd's of CPU2/3/4 and not to the DIE related sd's of CPU0/1.
    >>>
    >>> I thought so far that I can achieve that by getting rid of GDIE sd level
    >>> for CPU0/1 simply by choosing the cpu_foo_mask() function in such a way
    >>> that it returns the same cpu mask as its child sd level (MC) and of DIE
    >>> sd level for CPU2/3/4 because it returns the same cpu mask as its child
    >>> sd level (GDIE) related cpu mask function. This will let sd degenerate
    >>> do it's job of folding sd levels which it does. The only problem I have
    >>> is that the groups are not created correctly any more.
    >>>
    >>> I don't see right now how the flag SD_SHARE_FOO affects the code in
    >>> get_group()/build_sched_groups().
    >>>
    >>> Think of SD_SHARE_FOO of something I would like to have for all sd's of
    >>> CPU's of cluster 1 (CPU2/3/4) and not on cluster 0 (CPU0/1) in the sd
    >>> level where each CPU sees two groups (group0 containing CPU0/1 and
    >>> group1 containing CPU2/3/4 or vice versa) (GDIE/DIE) .
    >>
    >> I'm not sure that's it's feasible because it's not possible from a
    >> topology pov to have different flags if the span include all cpus.
    >> Could you give us more details about what you want to achieve with
    >> this flag ?
    >
    > IMHO, the flag is not important for this discussion. OTHA, information
    > like you can't use sd degenerate functionality to fold adjacent sd
    > levels (GFOO/FOO) on sd level which span all CPUs would be. I want to
    > make sure we understand what are the limitations to use folding of
    > adjacent sd levels based on per-cpu differences in the return value of
    > cpu_mask functions.
    >
    > -- Dietmar
    >
    > [...]
    >


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