sched/topology: Restore SD_PREFER_SIBLING on MC domains

The normal x86_topology on NHM+ machines degenerates because the MC
and CPU domains are of the same size, therefore MC inherits
SD_PREFER_SIBLING from CPU (which then gets taken out). The result is
that we'll spread tasks across the first NUMA level in order to
maximize cache utilization.

However, for the x86_numa_in_package_topology we loose the CPU domain,
and we'll not have SD_PREFER_SIBLING set anywhere, giving a distinct
difference in behaviour.

Commit:

  8e7fbcbc22c1 ("sched: Remove stale power aware scheduling remnants and dysfunctional knobs")

made a fail by not preserving the SD_PREFER_SIBLING for the !power_saving
case on both CPU and MC.

Then commit:

  6956dc568f34 ("sched/numa: Add SD_PERFER_SIBLING to CPU domain")

adds it back to the CPU but not MC.

Restore that now, such that we get consistent spreading behaviour wrt
L3 and NUMA.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index f1cf4f306a8285b642c02ebd28e4d0c78e21e9a5..86e81f06d36b3cdd859ed549e4640504c285f2c4 100644 (file)
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1157,6 +1157,7 @@ sd_init(struct sched_domain_topology_level *tl,
                sd->smt_gain = 1178; /* ~15% */
 
        } else if (sd->flags & SD_SHARE_PKG_RESOURCES) {
+               sd->flags |= SD_PREFER_SIBLING;
                sd->imbalance_pct = 117;
                sd->cache_nice_tries = 1;
                sd->busy_idx = 2;