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    SubjectRe: [PATCH v6 6/7] sched: add SD_BALANCE_NEWIDLE at MC and CPU level for sched_mc>0
    * Andrew Morton <akpm@linux-foundation.org> [2008-12-17 17:42:54]:

    > On Wed, 17 Dec 2008 22:57:38 +0530
    > Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> wrote:
    >
    > > --- a/include/linux/sched.h
    > > +++ b/include/linux/sched.h
    > > @@ -782,6 +782,16 @@ enum powersavings_balance_level {
    > > ((sched_mc_power_savings || sched_smt_power_savings) ? \
    > > SD_POWERSAVINGS_BALANCE : 0)
    >
    > What's with all the crappy macros in here?

    Hi Andrew,

    These macros set the SD_POWERSAVINGS_BALANCE flag based on the
    sysfs tunable.

    > > +/*
    > > + * Optimise SD flags for power savings:
    > > + * SD_BALANCE_NEWIDLE helps agressive task consolidation and power savings.
    > > + * Keep default SD flags if sched_{smt,mc}_power_saving=0
    > > + */
    > > +
    > > +#define POWERSAVING_SD_FLAGS \
    > > + ((sched_mc_power_savings || sched_smt_power_savings) ? \
    > > + SD_BALANCE_NEWIDLE : 0)
    >
    > This one purports to be a constant, but it isn't - it's code.
    >
    > It would be cleaner, clearer and more idiomatic to do
    >
    > static inline int powersaving_sd_flags(void)
    > {
    > ...
    > }

    Your are suggesting to move these to inline functions. I will write
    a patch and post for review.

    > Also, doing (sched_mc_power_savings | sched_smt_power_saving) might
    > save a branch.
    >
    > > #define test_sd_parent(sd, flag) ((sd->parent && \
    > > (sd->parent->flags & flag)) ? 1 : 0)
    >
    > buggy when passed an expression with side-effects. Doesn't need to be
    > implemented as a macro.

    Agreed, but these macros are used throughout sched.c and are
    performance sensitive. Inline functions are a close enough
    replacement for the macro let me look for any performance penalty as
    well and report.

    Thanks for the review and comments.

    --Vaidy


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