From 3ff70551a942b4c1d3c2e96e31a5c6e369a6d0be Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Fri, 3 Apr 2015 01:46:34 +0200 Subject: [PATCH] ACPI/PAD: Remove the local APIC nonsense While looking through the (ab)use of the clockevents_notify() function I stumbled over the following gem in the acpi_pad code: if (lapic_detected_unstable && !lapic_marked_unstable) { /* LAPIC could halt in idle, so notify users */ for_each_online_cpu(i) clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ON, &i); lapic_marked_unstable = 1; } This code calls on the cpu which detects the lapic unstable condition first clockevents_notify() to tell the core code that the broadcast should be enabled on all online cpus. Brilliant stuff that as it notifies the core code a num_online_cpus() times that the broadcast should be enabled on the current cpu. This probably has never been noticed because that code got never tested with NOHZ=n and HIGHRES_TIMER=n or it just worked by chance because one of the other mechanisms told the core in the right way that the local apic timer is wreckaged. Sigh, this is: - The 4th incarnation of idle drivers which has their own mechanism to detect and deal with X86_FEATURE_ARAT. - The 2nd incarnation of fake idle mechanisms with a different set of brainmelting bugs. - Has been merged against an explicit NAK of the scheduler maintainer with the promise to improve it over time. - Another example of featuritis driven trainwreck engineering. - Another pointless waste of my time. Fix this nonsense by removing that lapic detection and notification logic and simply call into the clockevents code unconditonally. The ARAT feature is marked in the lapic clockevent already so the core code will just ignore the requests and return. Signed-off-by: Thomas Gleixner Signed-off-by: Rafael J. Wysocki Cc: Peter Zijlstra Cc: Borislav Petkov Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1887788.RObRuI4tSv@vostro.rjw.lan Signed-off-by: Ingo Molnar --- drivers/acpi/acpi_pad.c | 26 +++++--------------------- 1 file changed, 5 insertions(+), 21 deletions(-) diff --git a/drivers/acpi/acpi_pad.c b/drivers/acpi/acpi_pad.c index c7b105c0e1d3..1686e9f756fd 100644 --- a/drivers/acpi/acpi_pad.c +++ b/drivers/acpi/acpi_pad.c @@ -41,8 +41,6 @@ static unsigned long power_saving_mwait_eax; static unsigned char tsc_detected_unstable; static unsigned char tsc_marked_unstable; -static unsigned char lapic_detected_unstable; -static unsigned char lapic_marked_unstable; static void power_saving_mwait_init(void) { @@ -82,13 +80,10 @@ static void power_saving_mwait_init(void) */ if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC)) tsc_detected_unstable = 1; - if (!boot_cpu_has(X86_FEATURE_ARAT)) - lapic_detected_unstable = 1; break; default: - /* TSC & LAPIC could halt in idle */ + /* TSC could halt in idle */ tsc_detected_unstable = 1; - lapic_detected_unstable = 1; } #endif } @@ -177,28 +172,17 @@ static int power_saving_thread(void *data) mark_tsc_unstable("TSC halts in idle"); tsc_marked_unstable = 1; } - if (lapic_detected_unstable && !lapic_marked_unstable) { - int i; - /* LAPIC could halt in idle, so notify users */ - for_each_online_cpu(i) - clockevents_notify( - CLOCK_EVT_NOTIFY_BROADCAST_ON, - &i); - lapic_marked_unstable = 1; - } + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ON, &cpu); + local_irq_disable(); cpu = smp_processor_id(); - if (lapic_marked_unstable) - clockevents_notify( - CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu); + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_ENTER, &cpu); stop_critical_timings(); mwait_idle_with_hints(power_saving_mwait_eax, 1); start_critical_timings(); - if (lapic_marked_unstable) - clockevents_notify( - CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu); + clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu); local_irq_enable(); if (time_before(expire_time, jiffies)) { -- 2.20.1