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    SubjectRe: + restore-missing-sysfs-max_cstate-attr.patch added to -mm tree
    Pallipadi, Venkatesh wrote:
    >> On Fri, 30 Nov 2007 14:06:55 -0800
    >> "Pallipadi, Venkatesh" <> wrote:
    >> Please dont go off-list like this. I put Mark's original
    >> mailing list cc's
    >> back.
    > Sorry for missing some cc's earlier. I blindly did a reply-all to the
    > mm-commits mail I got.
    >>> I will have to Nack this. The reason max_cstate was initentionally
    >>> removed due to couple of reasons:
    >> It broke userspace without any warning or migration period, afaict.
    > Yes. That's true. I will have to take the blame for that. It has been
    > known for a while during cpuidle development. But, it was never
    > documented as deprecating.
    >>> 1) All in kernel users of max_cstate should rather be using
    >>> pm_qos/latency interfaces. All such max_cstate usages must already be
    >>> migrated.
    >> That code isn't merged.
    > All kernel part is already merged. I mean, there are do drivers that
    > depend on max_cstate. They use latency_notifier thing today and their
    > migration to pm_qos part is not merged yet.
    >>> 2) Supporting max_cstate as a dynamic parameter cleanly is no longer
    >>> possible in acpi/processor_idle.c as the C-state policy has moved to
    >>> cpuidle instead. It can be done if it is needed. But, just
    >> below patch
    >>> will not really work with cpuidle.
    >>> Selecting max_cstate at boot time as a debug option still
    >> works without
    >>> this patch.
    >>> So, just this patch will not get back the functionality with cpuidle.
    >>> Infact changing it at run time will have no effect. Question
    >> however is:
    >>> Is there a real need to revive this parameter so that user can change
    >>> max_cstate at run time?
    >> It is not known whether Mark is actually writing to this
    >> thing. Perhaps
    >> read-only permissions would be a suitable fix?
    > Exporting it as read only should be OK. We also need to know if there
    > are hard user space dependency on writing to this from userspace.

    Well, actually.. my scripts have a firm need to write "1" to it,
    and then later restore the original value.

    This is needed to *greatly* speed up an otherwise sluggish binary I use,
    as well as whenever I want to semi-accurately benchmark I/O.

    Is there another way to achieve exactly the same behaviour?

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      Last update: 2007-12-01 03:55    [W:0.023 / U:109.288 seconds]
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