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Date: Thu, 8 May 2008 11:25:47 +0200
From: Ingo Molnar <mingo@elte.hu>
To: Mike Galbraith <efault@gmx.de>
Cc: "Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       LKML <linux-kernel@vger.kernel.org>
Subject: Re: sysbench+mysql(oltp, readonly) 30% regression with 2.6.26-rc1
Message-ID: <20080508092547.GA32574@elte.hu>
References: <1210136148.3453.59.camel@ymzhang> <1210177575.6525.4.camel@lappy.programming.kicks-ass.net> <1210228531.3453.124.camel@ymzhang> <1210233617.4895.6.camel@marge.simson.net> <20080508084607.GA31515@elte.hu>
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* Ingo Molnar <mingo@elte.hu> wrote:

> -	down(&kernel_sem);
> +	if (panic_timeout) {
> +		while (down_trylock(&kernel_sem))
> +			cpu_relax();

updated one below - this will work fine in the !panic_timeout case too 
;-)

	Ingo

Index: linux/lib/kernel_lock.c
===================================================================
--- linux.orig/lib/kernel_lock.c
+++ linux/lib/kernel_lock.c
@@ -46,7 +46,12 @@ int __lockfunc __reacquire_kernel_lock(v
 	task->lock_depth = -1;
 	preempt_enable_no_resched();
 
-	down(&kernel_sem);
+	if (panic_timeout) {
+		while (down_trylock(&kernel_sem))
+			cpu_relax();
+	} else {
+		down(&kernel_sem);
+	}
 
 	preempt_disable();
 	task->lock_depth = saved_lock_depth;
@@ -67,11 +72,17 @@ void __lockfunc lock_kernel(void)
 	struct task_struct *task = current;
 	int depth = task->lock_depth + 1;
 
-	if (likely(!depth))
+	if (likely(!depth)) {
 		/*
 		 * No recursion worries - we set up lock_depth _after_
 		 */
-		down(&kernel_sem);
+		if (panic_timeout) {
+			while (down_trylock(&kernel_sem))
+				cpu_relax();
+		} else {
+			down(&kernel_sem);
+		}
+	}
 
 	task->lock_depth = depth;
 }