linux-kernel - [PATCH RESEND] x86: Conditionally update time when ack-ing pending irqs

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Date:	Fri, 20 Apr 2012 01:12:32 +0300
From:	Ido Yariv <ido@...ery.com>
To:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	Shai Fultheim <shai@...lemp.com>, Ido Yariv <ido@...ery.com>
Subject: [PATCH RESEND] x86: Conditionally update time when ack-ing pending irqs

From: Shai Fultheim <shai@...lemp.com>

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>
[ido@...ery.com: rebased and reworded the commit message]
Signed-off-by: Ido Yariv <ido@...ery.com>
---
 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 11544d8..f0330f2 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);
 
-- 
1.7.7.6

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