linux-kernel - [RFC PATCH v2 1/3] sched/core: Introduce SD_ASYM_CPUCAPACITY_FULL sched

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Message-Id: <1619602363-1305-2-git-send-email-beata.michalska@arm.com>
Date:   Wed, 28 Apr 2021 10:32:41 +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 v2 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,
brought in by the newly introduced flag, 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