From: David Mosberger-Tang <davidm@hpl.hp.com>
Date: Wed, 4 May 2005 20:25:00 +0000 (-0700)
Subject: [IA64] Speed up lfetch.fault [NULL]
X-Git-Tag: v2.6.13-rc2~59^2~10
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=458f935527372499b714bf4f8e646a68bb0f52e3;p=linux-2.6

[IA64] Speed up lfetch.fault [NULL]

This patch greatly speeds up the handling of lfetch.fault instructions
which result in NaT consumption. Due to the NaT-page mapped at address
0, this is guaranteed to happen when lfetch.fault'ing a NULL pointer.
With this patch in place, we can even define prefetch()/prefetchw() as
lfetch.fault without significant performance degradation.  More
importantly, it allows compilers to be more aggressive with using
lfetch.fault on pointers that might be NULL.

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---

diff --git a/arch/ia64/kernel/ivt.S b/arch/ia64/kernel/ivt.S
index b28d2212a7..3bb3a13c40 100644
--- a/arch/ia64/kernel/ivt.S
+++ b/arch/ia64/kernel/ivt.S
@@ -1243,6 +1243,25 @@ END(disabled_fp_reg)
 // 0x5600 Entry 26 (size 16 bundles) Nat Consumption (11,23,37,50)
 ENTRY(nat_consumption)
 	DBG_FAULT(26)
+
+	mov r16=cr.ipsr
+	mov r17=cr.isr
+	mov r31=pr				// save PR
+	;;
+	and r18=0xf,r17				// r18 = cr.ipsr.code{3:0}
+	tbit.z p6,p0=r17,IA64_ISR_NA_BIT
+	;;
+	cmp.ne.or p6,p0=IA64_ISR_CODE_LFETCH,r18
+	dep r16=-1,r16,IA64_PSR_ED_BIT,1
+(p6)	br.cond.spnt 1f		// branch if (cr.ispr.na == 0 || cr.ipsr.code{3:0} != LFETCH)
+	;;
+	mov cr.ipsr=r16		// set cr.ipsr.na
+	mov pr=r31,-1
+	;;
+	rfi
+
+1:	mov pr=r31,-1
+	;;
 	FAULT(26)
 END(nat_consumption)