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Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with sched_domain_shared

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On Thu, May 12, 2016 at 12:05:37PM +1000, Michael Neuling wrote:
> On Wed, 2016-05-11 at 20:24 +0200, Peter Zijlstra wrote:
> > On Wed, May 11, 2016 at 02:33:45PM +0200, Peter Zijlstra wrote:
> > > 
> > > Hmm, PPC folks; what does your topology look like?
> > > 
> > > Currently your sched_domain_topology, as per arch/powerpc/kernel/smp.c
> > > seems to suggest your cores do not share cache at all.
> > > 
> > > https://en.wikipedia.org/wiki/POWER7 seems to agree and states
> > > 
> > >   "4 MB L3 cache per C1 core"
> > > 
> > > And http://www-03.ibm.com/systems/resources/systems_power_software_i_pe
> > > rfmgmt_underthehood.pdf
> > > also explicitly draws pictures with the L3 per core.
> > > 
> > > _however_, that same document describes L3 inter-core fill and lateral
> > > cast-out, which sounds like the L3s work together to form a node wide
> > > caching system.
> > > 
> > > Do we want to model this co-operative L3 slices thing as a sort of
> > > node-wide LLC for the purpose of the scheduler ?
> > Going back a generation; Power6 seems to have a shared L3 (off package)
> > between the two cores on the package. The current topology does not
> > reflect that at all.
> > 
> > And going forward a generation; Power8 seems to share the per-core
> > (chiplet) L3 amonst all cores (chiplets) + is has the centaur (memory
> > controller) 16M L4.
> 
> Yep, L1/L2/L3 is per core on POWER8 and POWER7.  POWER6 and POWER5 (both
> dual core chips) had a shared off chip cache

But as per the above, Power7 and Power8 have explicit logic to share the
per-core L3 with the other cores.

How effective is that? From some of the slides/documents i've looked at
the L3s are connected with a high-speed fabric. Suggesting that the
cross-core sharing should be fairly efficient.

In which case it would make sense to treat/model the combined L3 as a
single large LLC covering all cores.

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[RFC][PATCH 0/7] sched: select_idle_siblings rewrite Peter Zijlstra <peterz@infradead.org> - 2016-05-09 13:00 +0200
  [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-09 13:00 +0200
    Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-11 14:00 +0200
      Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-11 14:40 +0200
        Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-11 20:20 +0200
        Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-11 20:30 +0200
          Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Michael Neuling <mikey@neuling.org> - 2016-05-12 04:10 +0200
            Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-12 07:10 +0200
              Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Michael Neuling <mikey@neuling.org> - 2016-05-12 13:10 +0200
                Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-12 13:40 +0200
                Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Michael Neuling <mikey@neuling.org> - 2016-05-13 02:20 +0200
                Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-16 16:10 +0200
                Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-17 12:30 +0200
                Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Srikar Dronamraju <srikar@linux.vnet.ibm.com> - 2016-05-17 13:00 +0200
                Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-17 13:20 +0200
      Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-11 19:40 +0200
        Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-11 20:10 +0200
    Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-05-16 17:40 +0200
      Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-16 19:10 +0200
        Re: [RFC][PATCH 4/7] sched: Replace sd_busy/nr_busy_cpus with  sched_domain_shared Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-05-16 19:30 +0200
  [RFC][PATCH 1/7] sched: Remove unused @cpu argument from destroy_sched_domain*() Peter Zijlstra <peterz@infradead.org> - 2016-05-09 13:00 +0200
  [RFC][PATCH 3/7] sched: Introduce struct sched_domain_shared Peter Zijlstra <peterz@infradead.org> - 2016-05-09 13:00 +0200
  [RFC][PATCH 6/7] sched: Optimize SCHED_SMT Peter Zijlstra <peterz@infradead.org> - 2016-05-09 13:00 +0200
  Re: [RFC][PATCH 0/7] sched: select_idle_siblings rewrite Chris Mason <clm@fb.com> - 2016-05-10 03:00 +0200
  Re: [RFC][PATCH 0/7] sched: select_idle_siblings rewrite Chris Mason <clm@fb.com> - 2016-05-11 16:30 +0200
  [RFC][PATCH 8/7] sched/fair: Use utilization distance to filter  affine sync wakeups Mike Galbraith <mgalbraith@suse.de> - 2016-05-18 08:00 +0200
    Re: [RFC][PATCH 8/7] sched/fair: Use utilization distance to filter  affine sync wakeups Rik van Riel <riel@redhat.com> - 2016-05-19 23:50 +0200
      Re: [RFC][PATCH 8/7] sched/fair: Use utilization distance to filter  affine sync wakeups Mike Galbraith <mgalbraith@suse.de> - 2016-05-20 05:00 +0200
  Re: [RFC][PATCH 0/7] sched: select_idle_siblings rewrite Chris Mason <clm@fb.com> - 2016-05-25 17:00 +0200
    Re: [RFC][PATCH 0/7] sched: select_idle_siblings rewrite Peter Zijlstra <peterz@infradead.org> - 2016-05-25 18:30 +0200

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