linux-kernel - [PATCH 10/10] powerpc/smp: Add fallback flag to powerpc MC domain

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Message-Id: <20210422102326.35889-11-srikar@linux.vnet.ibm.com>
Date:   Thu, 22 Apr 2021 15:53:26 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>,
        Parth Shah <parth@...ux.ibm.com>
Subject: [PATCH 10/10] powerpc/smp: Add fallback flag to powerpc MC domain

Power 10 supports MC domain. Cores within the MC domain
aka hemisphere have lesser cache access latency compared to cache access
latency for cores across the neighbouring MC. Last level of cache for a
Power 10 is at Core (4 threads).
Now that scheduler supports fallback LLC domain, mark MC domain with
SD_FALLBACK_LLC flag. With this each SMT 4 core forms a pair (as
fallback LLC) with another SMT 4 core within the MC domain.

Cc: LKML <linux-kernel@...r.kernel.org>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc: Parth Shah <parth@...ux.ibm.com>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Valentin Schneider <valentin.schneider@....com>
Cc: Dietmar Eggemann <dietmar.eggemann@....com>
Cc: Mel Gorman <mgorman@...hsingularity.net>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Rik van Riel <riel@...riel.com>
Signed-off-by: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
---
 arch/powerpc/kernel/smp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 5a4d59a1070d..bc6386055cbe 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -950,6 +950,11 @@ static int powerpc_shared_cache_flags(void)
 	return SD_SHARE_PKG_RESOURCES;
 }
 
+static int powerpc_mc_flags(void)
+{
+	return SD_FALLBACK_LLC;
+}
+
 /*
  * We can't just pass cpu_l2_cache_mask() directly because
  * returns a non-const pointer and the compiler barfs on that.
@@ -986,7 +991,7 @@ static struct sched_domain_topology_level powerpc_topology[] = {
 	{ cpu_smt_mask, powerpc_smt_flags, SD_INIT_NAME(SMT) },
 #endif
 	{ shared_cache_mask, powerpc_shared_cache_flags, SD_INIT_NAME(CACHE) },
-	{ cpu_mc_mask, SD_INIT_NAME(MC) },
+	{ cpu_mc_mask, powerpc_mc_flags, SD_INIT_NAME(MC) },
 	{ cpu_cpu_mask, SD_INIT_NAME(DIE) },
 	{ NULL, },
 };
-- 
2.18.2