linux-kernel - Re: [RFC PATCH 11/11] sched: Add comments to find_busiest

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Message-ID: <20090325131046.GF516@elte.hu>
Date:	Wed, 25 Mar 2009 14:10:46 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Balbir Singh <balbir@...ibm.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 11/11] sched: Add comments to find_busiest_group()
	function.


* Gautham R Shenoy <ego@...ibm.com> wrote:

> On Wed, Mar 25, 2009 at 01:29:13PM +0100, Ingo Molnar wrote:
> > 
> > * Gautham R Shenoy <ego@...ibm.com> wrote:
> > 
> > > On Wed, Mar 25, 2009 at 02:44:27PM +0530, Gautham R Shenoy wrote:
> > > > Add /** style comments around find_busiest_group(). Also add a few explanatory
> > > >   */
> > > 
> > > <snip>
> > > 
> > > >  static struct sched_group *
> > > >  find_busiest_group(struct sched_domain *sd, int this_cpu,
> > > > @@ -3593,17 +3613,31 @@ find_busiest_group(struct sched_domain *sd, int this_cpu,
> > > >  	update_sd_lb_stats(sd, this_cpu, idle, sd_idle, cpus,
> > > >  					balance, &sds);
> > > > 
> > > > +	/* Cases where imbalance does not exist from POV of this_cpu */
> > > > +	/* 1) this_cpu is not the appropriate cpu to perform load balancing
> > > > +	 *    at this level.
> > > > +	 * 2) There is no busy sibling group to pull from.
> > > > +	 * 3) This group is the busiest group.
> > > > +	 * 4) This group is more busy than the avg busieness at this
> > > > +	 *    sched_domain.
> > > > +	 * 5) The imbalance is within the specified limit.
> > > > +	 * 6) Any rebalance would lead to ping-pong
> > > > +	 */
> > > >  	if (balance && !(*balance))
> > > >  		goto ret;
> > > > 
> > > > -	if (!sds.busiest || sds.this_load >= sds.max_load
> > > > -		|| sds.busiest_nr_running == 0)
> > > > +	if (!sds.busiest || sd.busiest_nr_running == 0)
> > > 			    ^^^^^^^^^^^^^^^^^^^^
> > > should have been sds.busiest_nr_running. Hence the build failure on tip.
> > > 
> > > I think I missed compile testing this last patch.
> > > 
> > > Ingo, could you revert commit 7b6340ef884aff69a54f8a530c73ad9da0a7c388 in
> > > tip/balancing and commit the following patch instead?
> > 
> > sure - i've amended it and started testing it locally. If it passes 
> > testing it should show up in tip:master.
> 
> Thanks!
> 
> Meanwhile I'll see if there are any regressions in 2.6.29 with 
> this patchset.

Just try tip:master please - there's a number of other scheduler 
changes and it would be nice to validate them together.

	Ingo
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