[PATCH 2/2] powerpc/topology: Override cpu_smt_mask

From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Mel Gorman <mgorman@techsingularity.net>,
	Rik van Riel <riel@surriel.com>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Michael Neuling <mikey@neuling.org>,
	Gautham R Shenoy <ego@linux.vnet.ibm.com>,
	Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
Subject: [PATCH 2/2] powerpc/topology: Override cpu_smt_mask
Date: Tue,  4 Aug 2020 09:03:07 +0530	[thread overview]
Message-ID: <20200804033307.76111-2-srikar@linux.vnet.ibm.com> (raw)
In-Reply-To: <20200804033307.76111-1-srikar@linux.vnet.ibm.com>

On Power9 a pair of cores can be presented by the firmware as a big-core
for backward compatibility reasons, with 4 threads per (small) core and 8
threads per big-core. cpu_smt_mask() should generally point to the cpu mask
of the (small)core.

In order to maintain userspace backward compatibility (with Power8 chips in
case of Power9) in enterprise Linux systems, the topology_sibling_cpumask
has to be set to big-core. Hence override the default cpu_smt_mask() to be
powerpc specific allowing for better scheduling behaviour on Power.

Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Cc: LKML <linux-kernel@vger.kernel.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Valentin Schneider <valentin.schneider@arm.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Vaidyanathan Srinivasan <svaidy@linux.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/cputhreads.h |  1 -
 arch/powerpc/include/asm/smp.h        | 13 +++++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/cputhreads.h b/arch/powerpc/include/asm/cputhreads.h
index deb99fd6e060..98c8bd155bf9 100644
--- a/arch/powerpc/include/asm/cputhreads.h
+++ b/arch/powerpc/include/asm/cputhreads.h
@@ -23,7 +23,6 @@
 extern int threads_per_core;
 extern int threads_per_subcore;
 extern int threads_shift;
-extern bool has_big_cores;
 extern cpumask_t threads_core_mask;
 #else
 #define threads_per_core	1
diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index 9cd0765633c5..d4bc28accb28 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -131,6 +131,19 @@ static inline struct cpumask *cpu_smallcore_mask(int cpu)
 
 extern int cpu_to_core_id(int cpu);
 
+extern bool has_big_cores;
+
+#define cpu_smt_mask cpu_smt_mask
+#ifdef CONFIG_SCHED_SMT
+static inline const struct cpumask *cpu_smt_mask(int cpu)
+{
+	if (has_big_cores)
+		return per_cpu(cpu_smallcore_map, cpu);
+
+	return per_cpu(cpu_sibling_map, cpu);
+}
+#endif /* CONFIG_SCHED_SMT */
+
 /* Since OpenPIC has only 4 IPIs, we use slightly different message numbers.
  *
  * Make sure this matches openpic_request_IPIs in open_pic.c, or what shows up
-- 
2.18.2

