linux-kernel - [RFC PATCH 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched

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Message-Id: <1618578085-29584-2-git-send-email-beata.michalska@arm.com>
Date:   Fri, 16 Apr 2021 14:01:23 +0100
From:   Beata Michalska <beata.michalska@....com>
To:     linux-kernel@...r.kernel.org
Cc:     peterz@...radead.org, mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, valentin.schneider@....com,
        dietmar.eggemann@....com, corbet@....net, linux-doc@...r.kernel.org
Subject: [RFC PATCH 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched_domain flag

Introducing new, complementary to SD_ASYM_CPUCAPACITY, sched_domain
topology flag, to distinguish between shed_domains where any CPU
capacity asymmetry is detected (SD_ASYM_CPUCAPACITY) and ones where
a full range of CPU capacities is visible to all domain members
(SD_ASYM_CPUCAPACITY_FULL).

With the distinction between full and partial CPU capacity asymmetry,
the scope of the original SD_ASYM_CPUCAPACITY flag gets shifted, still
maintaining the existing behaviour when one is detected on a given
sched domain, allowing misfit migrations within sched domains that
do not observe full range of CPU capacities but still do have members
with different capacity values. It loses though it's meaning when it
comes to the lowest CPU asymmetry sched_domain level per-cpu pointer,
which is to be now denoted by SD_ASYM_CPUCAPACITY_FULL flag.

Signed-off-by: Beata Michalska <beata.michalska@....com>
---
 include/linux/sched/sd_flags.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/sched/sd_flags.h b/include/linux/sched/sd_flags.h
index 34b21e9..57bde66 100644
--- a/include/linux/sched/sd_flags.h
+++ b/include/linux/sched/sd_flags.h
@@ -91,6 +91,16 @@ SD_FLAG(SD_WAKE_AFFINE, SDF_SHARED_CHILD)
 SD_FLAG(SD_ASYM_CPUCAPACITY, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS)

 /*
+ * Domain members have different CPU capacities spanning all unique CPU
+ * capacity values.
+ *
+ * SHARED_PARENT: Set from the topmost domain down to the first domain where
+ *		  all available CPU capacities are visible
+ * NEEDS_GROUPS: Per-CPU capacity is asymmetric between groups.
+ */
+SD_FLAG(SD_ASYM_CPUCAPACITY_FULL, SDF_SHARED_PARENT | SDF_NEEDS_GROUPS)
+
+/*
  * Domain members share CPU capacity (i.e. SMT)
  *
  * SHARED_CHILD: Set from the base domain up until spanned CPUs no longer share
-- 
2.7.4