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Message-ID: <87h6hq74j0.ffs@tglx>
Date: Fri, 01 Mar 2024 09:14:11 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: x86@...nel.org, Steven Rostedt <rostedt@...dmis.org>, "Paul E. McKenney"
<paulmck@...nel.org>
Subject: Re: [patch 6/6] x86/idle: Select idle routine only once
On Thu, Feb 29 2024 at 15:23, Thomas Gleixner wrote:
>
> - if (x86_idle_set())
> - return;
> -
Bah. With XEN=n this results in a defined but not used warning.
Updated version below.
---
Subject: x86/idle: Select idle routine only once
From: Thomas Gleixner <tglx@...utronix.de>
Date: Wed, 28 Feb 2024 23:20:32 +0100
The idle routine selection is done on every CPU bringup operation and has a
guard in place which is effective after the first invocation, which is a
pointless exercise.
Invoke it once on the boot CPU and mark the related functions __init.
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
V1a: Move x86_idle_set() into the only usage site (0day)
---
arch/x86/include/asm/processor.h | 2 +-
arch/x86/kernel/cpu/common.c | 4 ++--
arch/x86/kernel/process.c | 18 +++++-------------
3 files changed, 8 insertions(+), 16 deletions(-)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -555,7 +555,7 @@ static inline void load_sp0(unsigned lon
unsigned long __get_wchan(struct task_struct *p);
-extern void select_idle_routine(const struct cpuinfo_x86 *c);
+extern void select_idle_routine(void);
extern void amd_e400_c1e_apic_setup(void);
extern unsigned long boot_option_idle_override;
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1938,8 +1938,6 @@ static void identify_cpu(struct cpuinfo_
/* Init Machine Check Exception if available. */
mcheck_cpu_init(c);
- select_idle_routine(c);
-
#ifdef CONFIG_NUMA
numa_add_cpu(smp_processor_id());
#endif
@@ -2343,6 +2341,8 @@ void __init arch_cpu_finalize_init(void)
{
identify_boot_cpu();
+ select_idle_routine();
+
/*
* identify_boot_cpu() initialized SMT support information, let the
* core code know.
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -748,11 +748,6 @@ EXPORT_SYMBOL(default_idle);
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 __noreturn play_dead(void)
{
@@ -783,10 +778,9 @@ EXPORT_SYMBOL_GPL(arch_cpu_idle);
#ifdef CONFIG_XEN
bool xen_set_default_idle(void)
{
- bool ret = x86_idle_set();
+ bool ret = !!static_call_query(x86_idle);
static_call_update(x86_idle, default_idle);
-
return ret;
}
#endif
@@ -853,8 +847,9 @@ void __noreturn stop_this_cpu(void *dumm
* Do not prefer MWAIT if MONITOR instruction has a bug or idle=nomwait
* is passed to kernel commandline parameter.
*/
-static bool prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
+static __init bool prefer_mwait_c1_over_halt(void)
{
+ const struct cpuinfo_x86 *c = &boot_cpu_data;
u32 eax, ebx, ecx, edx;
/* If override is enforced on the command line, fall back to HALT. */
@@ -908,7 +903,7 @@ static __cpuidle void mwait_idle(void)
__current_clr_polling();
}
-void select_idle_routine(const struct cpuinfo_x86 *c)
+void __init select_idle_routine(void)
{
if (boot_option_idle_override == IDLE_POLL) {
if (IS_ENABLED(CONFIG_SMP) && smp_num_siblings > 1)
@@ -916,10 +911,7 @@ void select_idle_routine(const struct cp
return;
}
- if (x86_idle_set())
- return;
-
- if (prefer_mwait_c1_over_halt(c)) {
+ if (prefer_mwait_c1_over_halt()) {
pr_info("using mwait in idle threads\n");
static_call_update(x86_idle, mwait_idle);
} else if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
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