From: Ben Gras <ben@minix3.org>
Date: Wed, 22 Sep 2010 14:31:06 +0000 (+0000)
Subject: enable_fpu_exception() - only write cr0 if bit isn't already on.
X-Git-Tag: v3.2.0~820
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/rndc.html?a=commitdiff_plain;h=82d576c9ca471b4c4fe33969604a245ec06c845b;p=minix.git

enable_fpu_exception() - only write cr0 if bit isn't already on.

(NMI profiling results indicate this both is relatively expensive and
happens a lot unnecessarily if the fpu is in use.)
---

diff --git a/kernel/arch/i386/exception.c b/kernel/arch/i386/exception.c
index 86eb54101..7b3e1e378 100644
--- a/kernel/arch/i386/exception.c
+++ b/kernel/arch/i386/exception.c
@@ -285,7 +285,9 @@ PUBLIC void proc_stacktrace(struct proc *whichproc)
 
 PUBLIC void enable_fpu_exception(void)
 {
-	write_cr0(read_cr0() | I386_CR0_TS);
+	u32_t cr0 = read_cr0();
+	if(!(cr0 & I386_CR0_TS))
+		write_cr0(cr0 | I386_CR0_TS);
 }
 
 PUBLIC void disable_fpu_exception(void)