linux-kernel - [ 13/48] x86: Conditionally update time when ack-ing pending irqs

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Message-Id: <20150515080530.849422300@1wt.eu>
Date:	Fri, 15 May 2015 10:05:43 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Shai Fultheim <shai@...lemp.com>, Ido Yariv <ido@...ery.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Ben Hutchings <ben@...adent.org.uk>, Willy Tarreau <w@....eu>
Subject: [ 13/48] x86: Conditionally update time when ack-ing pending
 irqs

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

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

commit 42fa4250436304d4650fa271f37671f6cee24e08 upstream.

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>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
(cherry picked from commit c9f1417be9acae3a9867f8bdab2b7924d76cf6ac)

Signed-off-by: Willy Tarreau <w@....eu>
---
 arch/x86/kernel/apic/apic.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index 1d2d670..be4bf4c 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -1250,11 +1250,13 @@ 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);
 
-- 
1.7.12.2.21.g234cd45.dirty



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