linux-kernel - [tip:timers/core] ACPI/PAD: Remove the local APIC nonsense

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Date:	Fri, 3 Apr 2015 01:21:40 -0700
From:	tip-bot for Thomas Gleixner <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, bp@...en8.de, mingo@...nel.org,
	torvalds@...ux-foundation.org, rafael.j.wysocki@...el.com,
	linux-kernel@...r.kernel.org, peterz@...radead.org, hpa@...or.com
Subject: [tip:timers/core] ACPI/PAD: Remove the local APIC nonsense

Commit-ID:  3ff70551a942b4c1d3c2e96e31a5c6e369a6d0be
Gitweb:     http://git.kernel.org/tip/3ff70551a942b4c1d3c2e96e31a5c6e369a6d0be
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Fri, 3 Apr 2015 01:46:34 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 3 Apr 2015 08:44:31 +0200

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 <tglx@...utronix.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1887788.RObRuI4tSv@vostro.rjw.lan
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 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 c7b105c..1686e9f 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)) {
--
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