Re: Plumbers: Tweaking scheduler policy micro-conf RFP

[Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>]

* Peter Zijlstra <peterz@infradead.org> [2012-05-15 17:35:41]:

> On Tue, 2012-05-15 at 17:05 +0200, Vincent Guittot wrote:
> > On 15 May 2012 15:00, Peter Zijlstra <peterz@infradead.org> wrote:
> > > On Tue, 2012-05-15 at 14:57 +0200, Vincent Guittot wrote:
 
[snip]

> But really short, look at kernel/sched/core.c:default_topology[]
> 
> I'd like to get rid of sd_init_* into a single function like
> sd_numa_init(), this would mean all archs would need to do is provide a
> simple list of ever increasing masks that match their topology.

You are suggesting that the archs will provide sched/core a list of
masks equivalent to the number of sched domain levels that we need to
build.  The SDTL_SHARE_XXX flag will also be passed per mask in order
to decide the SD flags for that domain.

> To aid this we can add some SDTL_flags, initially I was thinking of:
> 
>  SDTL_SHARE_CORE	-- aka SMT
>  SDTL_SHARE_CACHE	-- LLC cache domain (typically multi-core)
>  SDTL_SHARE_MEMORY	-- NUMA-node (typically socket)
> 
> The 'performance' policy is typically to spread over shared resources so
> as to minimize contention on these.
> 
> If you want to add some power we need some extra flags, maybe something
> like:
> 
>  SDTL_SHARE_POWERLINE	-- power domain (typically socket)

Let me take a case of two-socket,quad-core,HT x86 (Nehalem):

SDTL_SHARE_POWERLINE should be passed along with a cpumask that
represents sd_init_CPU or cpu_cpu_mask today.  So the number of
domains we build per-cpu will depend on the topology and the
sched_powersavings settings. 

--Vaidy