linux-kernel - [PATCH 2/3] x86: halt secondary CPU if master doesn't wait on it

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Date:	Thu, 13 Mar 2014 15:25:19 +0100
From:	Igor Mammedov <imammedo@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	imammedo@...hat.com, bp@...e.de, paul.gortmaker@...driver.com,
	JBeulich@...e.com, prarit@...hat.com, drjones@...hat.com,
	toshi.kani@...com, x86@...nel.org, riel@...hat.com,
	gong.chen@...ux.intel.com
Subject: [PATCH 2/3] x86: halt secondary CPU if master doesn't wait on it

if during CPU hotplug master CPU had errors during
sending AP wake up IPIs, it fails hotplug operation.
But AP might start and spin on never set
cpu_callout_mask indefinitely, consuming power or
host VCPU resources needlessly.

On the other hand, master CPU marks AP with
BAD_APICID if hotplug attempt failed, so use this
fact to halt CPU to avoid needless spinning.

Signed-off-by: Igor Mammedov <imammedo@...hat.com>
---
 arch/x86/kernel/cpu/common.c |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index e048e87..9f07b8e 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1242,8 +1242,11 @@ void cpu_init(void)
 	 * wait till the master CPU completes it's STARTUP sequence,
 	 * and decides to wait till this AP boots
 	 */
-	while (!cpumask_test_cpu(cpu, cpu_callout_mask))
+	while (!cpumask_test_cpu(cpu, cpu_callout_mask)) {
 		cpu_relax();
+		if (per_cpu(x86_cpu_to_apicid, cpu) == BAD_APICID)
+			halt();
+	}
 
 	/*
 	 * Load microcode on this cpu if a valid microcode is available.
@@ -1345,8 +1348,11 @@ void cpu_init(void)
 	 * wait till the master CPU completes it's STARTUP sequence,
 	 * and decides to wait till this AP boots
 	 */
-	while (!cpumask_test_cpu(cpu, cpu_callout_mask))
+	while (!cpumask_test_cpu(cpu, cpu_callout_mask)) {
 		cpu_relax();
+		if (per_cpu(x86_cpu_to_apicid, cpu) == BAD_APICID)
+			halt();
+	}
 
 
 	show_ucode_info_early();
-- 
1.7.1

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