linux-kernel - [tip:sched/core] sched/topology: Remove the ::smt_gain field from 'struct sched

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Date:   Tue, 11 Dec 2018 07:31:24 -0800
From:   tip-bot for Vincent Guittot <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...nel.org, vincent.guittot@...aro.org,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        torvalds@...ux-foundation.org, hpa@...or.com, efault@....de
Subject: [tip:sched/core] sched/topology: Remove the ::smt_gain field from
 'struct sched_domain'

Commit-ID:  765d0af19f5f388a34bf4533378f8398b72ded46
Gitweb:     https://git.kernel.org/tip/765d0af19f5f388a34bf4533378f8398b72ded46
Author:     Vincent Guittot <vincent.guittot@...aro.org>
AuthorDate: Wed, 29 Aug 2018 15:19:11 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 11 Dec 2018 15:16:57 +0100

sched/topology: Remove the ::smt_gain field from 'struct sched_domain'

::smt_gain is used to compute the capacity of CPUs of a SMT core with the
constraint 1 < ::smt_gain < 2 in order to be able to compute number of CPUs
per core. The field has_free_capacity of struct numa_stat, which was the
last user of this computation of number of CPUs per core, has been removed
by:

  2d4056fafa19 ("sched/numa: Remove numa_has_capacity()")

We can now remove this constraint on core capacity and use the defautl value
SCHED_CAPACITY_SCALE for SMT CPUs. With this remove, SCHED_CAPACITY_SCALE
becomes the maximum compute capacity of CPUs on every systems. This should
help to simplify some code and remove fields like rd->max_cpu_capacity

Furthermore, arch_scale_cpu_capacity() is used with a NULL sd in several other
places in the code when it wants the capacity of a CPUs to scale
some metrics like in pelt, deadline or schedutil. In case on SMT, the value
returned is not the capacity of SMT CPUs but default SCHED_CAPACITY_SCALE.

So remove it.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1535548752-4434-4-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 include/linux/sched/topology.h | 1 -
 kernel/sched/sched.h           | 3 ---
 kernel/sched/topology.c        | 2 --
 3 files changed, 6 deletions(-)

diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index 6b9976180c1e..7fa0bc17cd8c 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -89,7 +89,6 @@ struct sched_domain {
 	unsigned int newidle_idx;
 	unsigned int wake_idx;
 	unsigned int forkexec_idx;
-	unsigned int smt_gain;
 
 	int nohz_idle;			/* NOHZ IDLE status */
 	int flags;			/* See SD_* */
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 9bde60a11805..ceb896404869 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1864,9 +1864,6 @@ unsigned long arch_scale_freq_capacity(int cpu)
 static __always_inline
 unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 {
-	if (sd && (sd->flags & SD_SHARE_CPUCAPACITY) && (sd->span_weight > 1))
-		return sd->smt_gain / sd->span_weight;
-
 	return SCHED_CAPACITY_SCALE;
 }
 #endif
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 8d7f15ba5916..7364e0b427b7 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -1133,7 +1133,6 @@ sd_init(struct sched_domain_topology_level *tl,
 
 		.last_balance		= jiffies,
 		.balance_interval	= sd_weight,
-		.smt_gain		= 0,
 		.max_newidle_lb_cost	= 0,
 		.next_decay_max_lb_cost	= jiffies,
 		.child			= child,
@@ -1164,7 +1163,6 @@ sd_init(struct sched_domain_topology_level *tl,
 
 	if (sd->flags & SD_SHARE_CPUCAPACITY) {
 		sd->imbalance_pct = 110;
-		sd->smt_gain = 1178; /* ~15% */
 
 	} else if (sd->flags & SD_SHARE_PKG_RESOURCES) {
 		sd->imbalance_pct = 117;