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From:   Jiaxun Yang <jiaxun.yang@flygoat.com>
To:     linux-mips@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, tsbogend@alpha.franken.de,
        linux-doc@vger.kernel.org, corbet@lwn.net,
        Jiaxun Yang <jiaxun.yang@flygoat.com>
Subject: [PATCH 1/3] MIPS: Rework smt cmdline parameters
Date:   Sun, 21 May 2023 23:31:22 +0100
Message-Id: <20230521223124.21911-2-jiaxun.yang@flygoat.com>
In-Reply-To: <20230521223124.21911-1-jiaxun.yang@flygoat.com>
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Provide a generic smt parameters interface aligned with s390
to allow users to limit smt usage and threads per core.

It replaced previous undocumented "nothreads" parameter for
smp-cps which is ambiguous and does not cover smp-mt.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
---
 .../admin-guide/kernel-parameters.txt          |  4 ++--
 arch/mips/include/asm/smp.h                    |  2 ++
 arch/mips/kernel/smp-cps.c                     | 13 +------------
 arch/mips/kernel/smp-mt.c                      |  3 ++-
 arch/mips/kernel/smp.c                         | 18 ++++++++++++++++++
 5 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 91963d3f0d5c..515cd1f88ea2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3830,7 +3830,7 @@
 	nosmp		[SMP] Tells an SMP kernel to act as a UP kernel,
 			and disable the IO APIC.  legacy for "maxcpus=0".
 
-	nosmt		[KNL,S390] Disable symmetric multithreading (SMT).
+	nosmt		[KNL,MIPS,S390] Disable symmetric multithreading (SMT).
 			Equivalent to smt=1.
 
 			[KNL,X86] Disable symmetric multithreading (SMT).
@@ -5743,7 +5743,7 @@
 				1: Fast pin select (default)
 				2: ATC IRMode
 
-	smt=		[KNL,S390] Set the maximum number of threads (logical
+	smt=		[KNL,MIPS,S390] Set the maximum number of threads (logical
 			CPUs) to use per physical CPU on systems capable of
 			symmetric multithreading (SMT). Will be capped to the
 			actual hardware limit.
diff --git a/arch/mips/include/asm/smp.h b/arch/mips/include/asm/smp.h
index aab8981bc32c..a40d8c0e4b87 100644
--- a/arch/mips/include/asm/smp.h
+++ b/arch/mips/include/asm/smp.h
@@ -57,6 +57,8 @@ extern int __cpu_logical_map[NR_CPUS];
 /* Mask of CPUs which are currently definitely operating coherently */
 extern cpumask_t cpu_coherent_mask;
 
+extern unsigned int smp_max_threads __initdata;
+
 extern asmlinkage void smp_bootstrap(void);
 
 extern void calculate_cpu_foreign_map(void);
diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index d7fdbec232da..474318bc08cb 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -25,24 +25,13 @@
 #include <asm/time.h>
 #include <asm/uasm.h>
 
-static bool threads_disabled;
 static DECLARE_BITMAP(core_power, NR_CPUS);
 
 struct core_boot_config *mips_cps_core_bootcfg;
 
-static int __init setup_nothreads(char *s)
-{
-	threads_disabled = true;
-	return 0;
-}
-early_param("nothreads", setup_nothreads);
-
 static unsigned core_vpe_count(unsigned int cluster, unsigned core)
 {
-	if (threads_disabled)
-		return 1;
-
-	return mips_cps_numvps(cluster, core);
+	return min(smp_max_threads, mips_cps_numvps(cluster, core));
 }
 
 static void __init cps_smp_setup(void)
diff --git a/arch/mips/kernel/smp-mt.c b/arch/mips/kernel/smp-mt.c
index 5f04a0141068..7729cc733421 100644
--- a/arch/mips/kernel/smp-mt.c
+++ b/arch/mips/kernel/smp-mt.c
@@ -46,7 +46,8 @@ static void __init smvp_copy_vpe_config(void)
 static unsigned int __init smvp_vpe_init(unsigned int tc, unsigned int mvpconf0,
 	unsigned int ncpu)
 {
-	if (tc > ((mvpconf0 & MVPCONF0_PVPE) >> MVPCONF0_PVPE_SHIFT))
+	if (tc >= smp_max_threads ||
+		(tc > ((mvpconf0 & MVPCONF0_PVPE) >> MVPCONF0_PVPE_SHIFT)))
 		return ncpu;
 
 	/* Deactivate all but VPE 0 */
diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 90c71d800b59..8fbef537fb88 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -73,6 +73,24 @@ static cpumask_t cpu_core_setup_map;
 
 cpumask_t cpu_coherent_mask;
 
+unsigned int smp_max_threads __initdata = UINT_MAX;
+
+static int __init early_nosmt(char *s)
+{
+	smp_max_threads = 1;
+	return 0;
+}
+early_param("nosmt", early_nosmt);
+
+static int __init early_smt(char *s)
+{
+	get_option(&s, &smp_max_threads);
+	/* Ensure at least one thread is available */
+	smp_max_threads = clamp_val(smp_max_threads, 1U, UINT_MAX);
+	return 0;
+}
+early_param("smt", early_smt);
+
 #ifdef CONFIG_GENERIC_IRQ_IPI
 static struct irq_desc *call_desc;
 static struct irq_desc *sched_desc;
-- 
2.39.2 (Apple Git-143)