linux-kernel - [tip:x86/apic] x86: Conditionally update time when ack-ing pending irqs

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Date:	Mon, 7 May 2012 21:24:56 -0700
From:	tip-bot for Shai Fultheim <shai@...lemp.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	shai@...lemp.com, ido@...ery.com, tglx@...utronix.de
Subject: [tip:x86/apic] x86:
  Conditionally update time when ack-ing pending irqs

Commit-ID:  42fa4250436304d4650fa271f37671f6cee24e08
Gitweb:     http://git.kernel.org/tip/42fa4250436304d4650fa271f37671f6cee24e08
Author:     Shai Fultheim <shai@...lemp.com>
AuthorDate: Fri, 20 Apr 2012 01:12:32 +0300
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 7 May 2012 16:25:28 +0200

x86: Conditionally update time when ack-ing pending irqs

On virtual environments, apic_read could take a long time. As a
result, under certain conditions the ack pending loop may exit
without any queued irqs left, but after more than one second. A
warning will be printed needlessly in this case.

If the loop is about to exit regardless of max_loops, don't
update it.

Signed-off-by: Shai Fultheim <shai@...lemp.com>
[ rebased and reworded the commit message]
Signed-off-by: Ido Yariv <ido@...ery.com>
Acked-by: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1334873552-31346-1-git-send-email-ido@wizery.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/apic/apic.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index edc2448..3beab62 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1325,11 +1325,13 @@ void __cpuinit setup_local_APIC(void)
 			       acked);
 			break;
 		}
-		if (cpu_has_tsc) {
-			rdtscll(ntsc);
-			max_loops = (cpu_khz << 10) - (ntsc - tsc);
-		} else
-			max_loops--;
+		if (queued) {
+			if (cpu_has_tsc) {
+				rdtscll(ntsc);
+				max_loops = (cpu_khz << 10) - (ntsc - tsc);
+			} else
+				max_loops--;
+		}
 	} while (queued && max_loops > 0);
 	WARN_ON(max_loops <= 0);
 
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