linux-kernel - [tip:sched/urgent] Revert "x86, timers: Check for pending timers after (device) interrupts"

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Date:	Fri, 9 Oct 2009 14:23:35 GMT
From:	tip-bot for Ingo Molnar <mingo@...e.hu>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	torvalds@...ux-foundation.org, arjan@...ux.intel.com,
	efault@....de, elendil@...net.nl, peterz@...radead.org,
	tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/urgent] Revert "x86, timers: Check for pending timers after (device) interrupts"

Commit-ID:  e7ab0f7b50bc4688fb5cf65de5d42e3b882fb8d1
Gitweb:     http://git.kernel.org/tip/e7ab0f7b50bc4688fb5cf65de5d42e3b882fb8d1
Author:     Ingo Molnar <mingo@...e.hu>
AuthorDate: Fri, 9 Oct 2009 15:58:20 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Fri, 9 Oct 2009 15:58:20 +0200

Revert "x86, timers: Check for pending timers after (device) interrupts"

This reverts commit 9bcbdd9c58617f1301dd4f17c738bb9bc73aca70.

The real bug producing LatencyTop latencies has been fixed in:

  f5dc375: sched: Update the clock of runqueue select_task_rq() selected

And the commit being reverted here triggers local timer processing
from every device IRQ. If device IRQs come in at a high frequency,
this could cause a performance regression.

The commit being reverted here purely 'fixed' the reported latency
as a side effect, because CPUs were being moved out of idle more
often.

Acked-by: Peter Zijlstra <peterz@...radead.org>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Frans Pop <elendil@...net.nl>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mike Galbraith <efault@....de>
Cc: Thomas Gleixner <tglx@...utronix.de>
LKML-Reference: <20091008064041.67219b13@...radead.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/irq.c |    2 --
 arch/x86/kernel/smp.c |    1 -
 2 files changed, 0 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 3912061..74656d1 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -244,7 +244,6 @@ unsigned int __irq_entry do_IRQ(struct pt_regs *regs)
 				__func__, smp_processor_id(), vector, irq);
 	}
 
-	run_local_timers();
 	irq_exit();
 
 	set_irq_regs(old_regs);
@@ -269,7 +268,6 @@ void smp_generic_interrupt(struct pt_regs *regs)
 	if (generic_interrupt_extension)
 		generic_interrupt_extension();
 
-	run_local_timers();
 	irq_exit();
 
 	set_irq_regs(old_regs);
diff --git a/arch/x86/kernel/smp.c b/arch/x86/kernel/smp.c
index d915d95..ec1de97 100644
--- a/arch/x86/kernel/smp.c
+++ b/arch/x86/kernel/smp.c
@@ -198,7 +198,6 @@ void smp_reschedule_interrupt(struct pt_regs *regs)
 {
 	ack_APIC_irq();
 	inc_irq_stat(irq_resched_count);
-	run_local_timers();
 	/*
 	 * KVM uses this interrupt to force a cpu out of guest mode
 	 */
--
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