Re: 143e1e28 sched: Rework sched_domain topology definition

[Mike Galbraith <umgwanakikbuti@gmail.com>]

On Sun, 2014-07-20 at 09:05 +0200, Mike Galbraith wrote: 
> On Sun, 2014-07-20 at 08:52 +0200, Peter Zijlstra wrote: 
> > On Sun, Jul 20, 2014 at 08:43:36AM +0200, Mike Galbraith wrote:
> > > Hi,
> > > 
> > > +/*
> > > + * Topology list, bottom-up.
> > > + */
> > > +static struct sched_domain_topology_level default_topology[] = {
> > > +#ifdef CONFIG_SCHED_SMT
> > > +	{ cpu_smt_mask, cpu_smt_flags, SD_INIT_NAME(SMT) },
> > > +#endif
> > > +#ifdef CONFIG_SCHED_MC
> > > +	{ cpu_coregroup_mask, cpu_core_flags, SD_INIT_NAME(MC) },
> > > +#endif
> > > +#ifdef CONFIG_SCHED_BOOK
> > > +	{ cpu_book_mask, SD_INIT_NAME(BOOK) },
> > > +#endif
> > > +	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },
> > > +	{ NULL, },
> > > +};
> > > 
> > > Why did this commit rename the CPU domain to DIE?
> > 
> > Because they're both wrong, but we found that DIE was less wrong than
> > CPU.
> 
> Ok, doesn't matter anyway, just looks peculiar.
> 
> > Seeing how CPU typically means 1 logical, well, CPU, in the scheduler,
> > and not the package you stick on your board.
> > 
> > We chose DIE over PACKAGE due to 1) its shorter name and 2) things like
> > interlagos which have multiple DIEs in one PACKAGE etc..
> 
> It's actually a good name for some NUMA topologies.  You don't ever want
> to see a CPU domain, that sucks cycles, so calling it DIE is fine :)

Like this 8 socket box.  CPU domain with weight 64 stings.

vogelweide:~/:[0]# tune-sched-domains
usage: tune-sched-domains <val>
{cpu0/domain0:MC} SD flag: 559
+   1: SD_LOAD_BALANCE:          Do load balancing on this domain
+   2: SD_BALANCE_NEWIDLE:       Balance when about to become idle
+   4: SD_BALANCE_EXEC:          Balance on exec
+   8: SD_BALANCE_FORK:          Balance on fork, clone
-  16: SD_BALANCE_WAKE:          Wake to idle CPU on task wakeup
+  32: SD_WAKE_AFFINE:           Wake task to waking CPU
-  64: SD_PREFER_LOCAL:          Prefer to keep tasks local to this domain
- 128: SD_SHARE_CPUPOWER:        Domain members share cpu power
- 256: SD_POWERSAVINGS_BALANCE:  Balance for power savings
+ 512: SD_SHARE_PKG_RESOURCES:   Domain members share cpu pkg resources
-1024: SD_SERIALIZE:             Only a single load balancing instance
-2048: SD_ASYM_PACKING:          Place busy groups earlier in the domain
-4096: SD_PREFER_SIBLING:        Prefer to place tasks in a sibling domain
-8192: SD_PREFER_UTILIZATION:    Prefer utilization over SMP nice
{cpu0/domain1:CPU} SD flag: 4143
+   1: SD_LOAD_BALANCE:          Do load balancing on this domain
+   2: SD_BALANCE_NEWIDLE:       Balance when about to become idle
+   4: SD_BALANCE_EXEC:          Balance on exec
+   8: SD_BALANCE_FORK:          Balance on fork, clone
-  16: SD_BALANCE_WAKE:          Wake to idle CPU on task wakeup
+  32: SD_WAKE_AFFINE:           Wake task to waking CPU
-  64: SD_PREFER_LOCAL:          Prefer to keep tasks local to this domain
- 128: SD_SHARE_CPUPOWER:        Domain members share cpu power
- 256: SD_POWERSAVINGS_BALANCE:  Balance for power savings
- 512: SD_SHARE_PKG_RESOURCES:   Domain members share cpu pkg resources
-1024: SD_SERIALIZE:             Only a single load balancing instance
-2048: SD_ASYM_PACKING:          Place busy groups earlier in the domain
+4096: SD_PREFER_SIBLING:        Prefer to place tasks in a sibling domain
-8192: SD_PREFER_UTILIZATION:    Prefer utilization over SMP nice