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SubjectRe: [PATCH v6 6/7] sched: add SD_BALANCE_NEWIDLE at MC and CPU level for sched_mc>0
* Ingo Molnar <mingo@elte.hu> [2008-12-18 13:46:44]:

>
> * Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com> wrote:
>
> > * 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.
>
> those macros are historic so feel free to convert them to inlines without
> re-measuring performance impact.

Sure Ingo. I will go ahead and change them in my next iteration.

> The patchset looks pretty good in principle otherwise, so if you could
> address Andrew's comments and clean up those bits in the next iteration we
> could start testing it in the scheduler tree. (Please also add Balbir
> Singh's acks to the next iteration.)

Thank you for acking the patch. I will address Andrew's comments and
post the next iteration along with Balbir's acks.

> and please fix your mailer to not inject stuff like this:
>
> Mail-Followup-To: Andrew Morton <akpm@linux-foundation.org>,
> linux-kernel@vger.kernel.org, suresh.b.siddha@intel.com,
> venkatesh.pallipadi@intel.com, a.p.zijlstra@chello.nl,
> mingo@elte.hu, dipankar@in.ibm.com, balbir@linux.vnet.ibm.com,
> vatsa@linux.vnet.ibm.com, ego@in.ibm.com, andi@firstfloor.org,
> davecb@sun.com, tconnors@astro.swin.edu.au, maxk@qualcomm.com,
> gregory.haskins@gmail.com, pavel@suse.cz
>
> It utterly messed up the addressing mode of my reply here and i had to
> edit the raw email headers manually to fix it up ;-)

OOPS! My bad mutt config! I have tried to fix this. Hopefully this
will not cause trouble anymore.

Thanks,
Vaidy


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