linux-kernel - Re: [PATCH v6 6/7] sched: add SD_BALANCE_NEWIDLE at MC and CPU level for sched

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Message-ID: <20081218152230.GA22463@dirshya.in.ibm.com>
Date:	Thu, 18 Dec 2008 20:52:30 +0530
From:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com,
	venkatesh.pallipadi@...el.com, a.p.zijlstra@...llo.nl,
	dipankar@...ibm.com, balbir@...ux.vnet.ibm.com,
	vatsa@...ux.vnet.ibm.com, ego@...ibm.com, andi@...stfloor.org,
	davecb@....com, tconnors@...ro.swin.edu.au, maxk@...lcomm.com,
	gregory.haskins@...il.com, pavel@...e.cz
Subject: Re: [PATCH v6 6/7] sched: add SD_BALANCE_NEWIDLE at MC and CPU
	level for sched_mc>0

* Ingo Molnar <mingo@...e.hu> [2008-12-18 13:46:44]:

> 
> * Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:
> 
> > * Andrew Morton <akpm@...ux-foundation.org> [2008-12-17 17:42:54]:
> > 
> > > On Wed, 17 Dec 2008 22:57:38 +0530
> > > Vaidyanathan Srinivasan <svaidy@...ux.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@...ux-foundation.org>,
>         linux-kernel@...r.kernel.org, suresh.b.siddha@...el.com,
>         venkatesh.pallipadi@...el.com, a.p.zijlstra@...llo.nl,
>         mingo@...e.hu, dipankar@...ibm.com, balbir@...ux.vnet.ibm.com,
>         vatsa@...ux.vnet.ibm.com, ego@...ibm.com, andi@...stfloor.org,
>         davecb@....com, tconnors@...ro.swin.edu.au, maxk@...lcomm.com,
>         gregory.haskins@...il.com, pavel@...e.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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