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Date:   Mon, 19 Sep 2022 11:59:41 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     peterz@...radead.org
Cc:     richard.henderson@...aro.org, ink@...assic.park.msu.ru,
        mattst88@...il.com, vgupta@...nel.org, linux@...linux.org.uk,
        ulli.kroll@...glemail.com, linus.walleij@...aro.org,
        shawnguo@...nel.org, Sascha Hauer <s.hauer@...gutronix.de>,
        kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
        tony@...mide.com, khilman@...nel.org, catalin.marinas@....com,
        will@...nel.org, guoren@...nel.org, bcain@...cinc.com,
        chenhuacai@...nel.org, kernel@...0n.name, geert@...ux-m68k.org,
        sammy@...my.net, monstr@...str.eu, tsbogend@...ha.franken.de,
        dinguyen@...nel.org, jonas@...thpole.se,
        stefan.kristiansson@...nalahti.fi, shorne@...il.com,
        James.Bottomley@...senPartnership.com, deller@....de,
        mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu,
        paul.walmsley@...ive.com, palmer@...belt.com,
        aou@...s.berkeley.edu, hca@...ux.ibm.com, gor@...ux.ibm.com,
        agordeev@...ux.ibm.com, borntraeger@...ux.ibm.com,
        svens@...ux.ibm.com, ysato@...rs.sourceforge.jp, dalias@...c.org,
        davem@...emloft.net, richard@....at,
        anton.ivanov@...bridgegreys.com, johannes@...solutions.net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        acme@...nel.org, mark.rutland@....com,
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        namhyung@...nel.org, jgross@...e.com, srivatsa@...il.mit.edu,
        amakhalov@...are.com, pv-drivers@...are.com,
        boris.ostrovsky@...cle.com, chris@...kel.net, jcmvbkbc@...il.com,
        rafael@...nel.org, lenb@...nel.org, pavel@....cz,
        gregkh@...uxfoundation.org, mturquette@...libre.com,
        sboyd@...nel.org, daniel.lezcano@...aro.org, lpieralisi@...nel.org,
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        anup@...infault.org, thierry.reding@...il.com,
        jonathanh@...dia.com, jacob.jun.pan@...ux.intel.com,
        atishp@...shpatra.org, Arnd Bergmann <arnd@...db.de>,
        yury.norov@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk, dennis@...nel.org, tj@...nel.org,
        cl@...ux.com, rostedt@...dmis.org, pmladek@...e.com,
        senozhatsky@...omium.org, john.ogness@...utronix.de,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, bsegall@...gle.com, mgorman@...e.de,
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        ryabinin.a.a@...il.com, glider@...gle.com, andreyknvl@...il.com,
        dvyukov@...gle.com, vincenzo.frascino@....com,
        Andrew Morton <akpm@...ux-foundation.org>, jpoimboe@...nel.org,
        linux-alpha@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org, linux-omap@...r.kernel.org,
        linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org,
        linux-ia64@...r.kernel.org, loongarch@...ts.linux.dev,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        openrisc@...ts.librecores.org, linux-parisc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org,
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        sparclinux@...r.kernel.org, linux-um@...ts.infradead.org,
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        virtualization@...ts.linux-foundation.org,
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        linux-arch@...r.kernel.org, kasan-dev@...glegroups.com,
        Frederic Weisbecker <frederic@...nel.org>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: [PATCH v2 02/44] x86/idle: Replace x86_idle 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>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 arch/x86/kernel/process.c |   50 +++++++++++++++++++++++++---------------------
 1 file changed, 28 insertions(+), 22 deletions(-)

--- 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>
@@ -692,7 +693,23 @@ void __switch_to_xtra(struct task_struct
 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)
@@ -715,28 +732,17 @@ 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;
 }
@@ -859,20 +865,20 @@ void select_idle_routine(const struct cp
 	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)
@@ -925,7 +931,7 @@ 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")) {
 		/*


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