linux-kernel - [tip: sched/core] x86/idle: Replace 'x86_idle' function pointer with a static

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Date:   Fri, 13 Jan 2023 12:31:16 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Tony Lindgren <tony@...mide.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] x86/idle: Replace 'x86_idle' function pointer with
 a static_call

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     aaa3896b969bdf946e0fd6aa6199da17b5da8d5c
Gitweb:        https://git.kernel.org/tip/aaa3896b969bdf946e0fd6aa6199da17b5da8d5c
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 12 Jan 2023 20:43:16 +01:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Fri, 13 Jan 2023 11:03:21 +01:00

x86/idle: Replace 'x86_idle' function pointer with a static_call

Typical boot time setup; no need to suffer an indirect call for that.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Tested-by: Tony Lindgren <tony@...mide.com>
Tested-by: Ulf Hansson <ulf.hansson@...aro.org>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Link: https://lore.kernel.org/r/20230112195539.453613251@infradead.org
---
 arch/x86/kernel/process.c | 50 +++++++++++++++++++++-----------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 40d156a..8481fbe 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -24,6 +24,7 @@
 #include <linux/cpuidle.h>
 #include <linux/acpi.h>
 #include <linux/elf-randomize.h>
+#include <linux/static_call.h>
 #include <trace/events/power.h>
 #include <linux/hw_breakpoint.h>
 #include <asm/cpu.h>
@@ -694,7 +695,23 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p)
 unsigned long boot_option_idle_override = IDLE_NO_OVERRIDE;
 EXPORT_SYMBOL(boot_option_idle_override);
 
-static void (*x86_idle)(void);
+/*
+ * We use this if we don't have any better idle routine..
+ */
+void __cpuidle default_idle(void)
+{
+	raw_safe_halt();
+}
+#if defined(CONFIG_APM_MODULE) || defined(CONFIG_HALTPOLL_CPUIDLE_MODULE)
+EXPORT_SYMBOL(default_idle);
+#endif
+
+DEFINE_STATIC_CALL_NULL(x86_idle, default_idle);
+
+static bool x86_idle_set(void)
+{
+	return !!static_call_query(x86_idle);
+}
 
 #ifndef CONFIG_SMP
 static inline void play_dead(void)
@@ -717,28 +734,17 @@ void arch_cpu_idle_dead(void)
 /*
  * Called from the generic idle code.
  */
-void arch_cpu_idle(void)
-{
-	x86_idle();
-}
-
-/*
- * We use this if we don't have any better idle routine..
- */
-void __cpuidle default_idle(void)
+void __cpuidle arch_cpu_idle(void)
 {
-	raw_safe_halt();
+	static_call(x86_idle)();
 }
-#if defined(CONFIG_APM_MODULE) || defined(CONFIG_HALTPOLL_CPUIDLE_MODULE)
-EXPORT_SYMBOL(default_idle);
-#endif
 
 #ifdef CONFIG_XEN
 bool xen_set_default_idle(void)
 {
-	bool ret = !!x86_idle;
+	bool ret = x86_idle_set();
 
-	x86_idle = default_idle;
+	static_call_update(x86_idle, default_idle);
 
 	return ret;
 }
@@ -880,20 +886,20 @@ void select_idle_routine(const struct cpuinfo_x86 *c)
 	if (boot_option_idle_override == IDLE_POLL && smp_num_siblings > 1)
 		pr_warn_once("WARNING: polling idle and HT enabled, performance may degrade\n");
 #endif
-	if (x86_idle || boot_option_idle_override == IDLE_POLL)
+	if (x86_idle_set() || boot_option_idle_override == IDLE_POLL)
 		return;
 
 	if (boot_cpu_has_bug(X86_BUG_AMD_E400)) {
 		pr_info("using AMD E400 aware idle routine\n");
-		x86_idle = amd_e400_idle;
+		static_call_update(x86_idle, amd_e400_idle);
 	} else if (prefer_mwait_c1_over_halt(c)) {
 		pr_info("using mwait in idle threads\n");
-		x86_idle = mwait_idle;
+		static_call_update(x86_idle, mwait_idle);
 	} else if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
 		pr_info("using TDX aware idle routine\n");
-		x86_idle = tdx_safe_halt;
+		static_call_update(x86_idle, tdx_safe_halt);
 	} else
-		x86_idle = default_idle;
+		static_call_update(x86_idle, default_idle);
 }
 
 void amd_e400_c1e_apic_setup(void)
@@ -946,7 +952,7 @@ static int __init idle_setup(char *str)
 		 * To continue to load the CPU idle driver, don't touch
 		 * the boot_option_idle_override.
 		 */
-		x86_idle = default_idle;
+		static_call_update(x86_idle, default_idle);
 		boot_option_idle_override = IDLE_HALT;
 	} else if (!strcmp(str, "nomwait")) {
 		/*