From a18d098f2aab82abde1d59c56aef9beca01c892b Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Thu, 5 Jun 2025 17:09:35 +0200 Subject: [PATCH] Reapply "x86/smp: Eliminate mwait_play_dead_cpuid_hint()" Revert commit 70523f335734 ("Revert "x86/smp: Eliminate mwait_play_dead_cpuid_hint()"") to reapply the changes from commit 96040f7273e2 ("x86/smp: Eliminate mwait_play_dead_cpuid_hint()") reverted by it. Previously, these changes caused idle power to rise on systems booting with "nosmt" in the kernel command line because they effectively caused "dead" SMT siblings to remain in idle state C1 after executing the HLT instruction, which prevented the processor from reaching package idle states deeper than PC2 going forward. Now, the "dead" SMT siblings are rescanned after initializing a proper cpuidle driver for the processor (either intel_idle or ACPI idle), at which point they are able to enter a sufficiently deep idle state in native_play_dead() via cpuidle, so the code changes in question can be reapplied. Signed-off-by: Rafael J. Wysocki Acked-by: Dave Hansen Tested-by: Artem Bityutskiy Link: https://patch.msgid.link/7813065.EvYhyI6sBW@rjwysocki.net --- arch/x86/kernel/smpboot.c | 54 +++++---------------------------------- 1 file changed, 7 insertions(+), 47 deletions(-) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index fc78c2325fd29..58ede3fa6a75b 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1244,6 +1244,10 @@ void play_dead_common(void) local_irq_disable(); } +/* + * We need to flush the caches before going to sleep, lest we have + * dirty data in our caches when we come back up. + */ void __noreturn mwait_play_dead(unsigned int eax_hint) { struct mwait_cpu_dead *md = this_cpu_ptr(&mwait_cpu_dead); @@ -1289,50 +1293,6 @@ void __noreturn mwait_play_dead(unsigned int eax_hint) } } -/* - * We need to flush the caches before going to sleep, lest we have - * dirty data in our caches when we come back up. - */ -static inline void mwait_play_dead_cpuid_hint(void) -{ - unsigned int eax, ebx, ecx, edx; - unsigned int highest_cstate = 0; - unsigned int highest_subcstate = 0; - int i; - - if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD || - boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) - return; - if (!this_cpu_has(X86_FEATURE_MWAIT)) - return; - if (!this_cpu_has(X86_FEATURE_CLFLUSH)) - return; - - eax = CPUID_LEAF_MWAIT; - ecx = 0; - native_cpuid(&eax, &ebx, &ecx, &edx); - - /* - * eax will be 0 if EDX enumeration is not valid. - * Initialized below to cstate, sub_cstate value when EDX is valid. - */ - if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED)) { - eax = 0; - } else { - edx >>= MWAIT_SUBSTATE_SIZE; - for (i = 0; i < 7 && edx; i++, edx >>= MWAIT_SUBSTATE_SIZE) { - if (edx & MWAIT_SUBSTATE_MASK) { - highest_cstate = i; - highest_subcstate = edx & MWAIT_SUBSTATE_MASK; - } - } - eax = (highest_cstate << MWAIT_SUBSTATE_SIZE) | - (highest_subcstate - 1); - } - - mwait_play_dead(eax); -} - /* * Kick all "offline" CPUs out of mwait on kexec(). See comment in * mwait_play_dead(). @@ -1383,9 +1343,9 @@ void native_play_dead(void) play_dead_common(); tboot_shutdown(TB_SHUTDOWN_WFS); - mwait_play_dead_cpuid_hint(); - if (cpuidle_play_dead()) - hlt_play_dead(); + /* Below returns only on error. */ + cpuidle_play_dead(); + hlt_play_dead(); } #else /* ... !CONFIG_HOTPLUG_CPU */ -- 2.39.5