linux-kernel - [PATCH v8 01/23] powerpc/8xx: Save r3 all the time in DTLB miss handler

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Message-Id: <ce64a208704307609589b1f54a71fd1423ac339f.1455032446.git.christophe.leroy@c-s.fr>
Date:	Tue,  9 Feb 2016 17:07:48 +0100 (CET)
From:	Christophe Leroy <christophe.leroy@....fr>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Scott Wood <oss@...error.net>
Cc:	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: [PATCH v8 01/23] powerpc/8xx: Save r3 all the time in DTLB miss
 handler

We are spending between 40 and 160 cycles with a mean of 65 cycles in
the DTLB handling routine (measured with mftbl) so make it more
simple althought it adds one instruction.
With this modification, we get three registers available at all time,
which will help with following patch.

Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
---
v2: no change
v3: no change
v4: no change
v5: no change
v6: no change
v8: no change

 arch/powerpc/kernel/head_8xx.S | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/kernel/head_8xx.S b/arch/powerpc/kernel/head_8xx.S
index e629e28..a89492e 100644
--- a/arch/powerpc/kernel/head_8xx.S
+++ b/arch/powerpc/kernel/head_8xx.S
@@ -385,23 +385,20 @@ InstructionTLBMiss:
 
 	. = 0x1200
 DataStoreTLBMiss:
-#ifdef CONFIG_8xx_CPU6
 	mtspr	SPRN_SPRG_SCRATCH2, r3
-#endif
 	EXCEPTION_PROLOG_0
-	mfcr	r10
+	mfcr	r3
 
 	/* If we are faulting a kernel address, we have to use the
 	 * kernel page tables.
 	 */
-	mfspr	r11, SPRN_MD_EPN
-	IS_KERNEL(r11, r11)
+	mfspr	r10, SPRN_MD_EPN
+	IS_KERNEL(r11, r10)
 	mfspr	r11, SPRN_M_TW	/* Get level 1 table */
 	BRANCH_UNLESS_KERNEL(3f)
 	lis	r11, (swapper_pg_dir-PAGE_OFFSET)@ha
 3:
-	mtcr	r10
-	mfspr	r10, SPRN_MD_EPN
+	mtcr	r3
 
 	/* Insert level 1 index */
 	rlwimi	r11, r10, 32 - ((PAGE_SHIFT - 2) << 1), (PAGE_SHIFT - 2) << 1, 29
@@ -453,9 +450,7 @@ DataStoreTLBMiss:
 	MTSPR_CPU6(SPRN_MD_RPN, r10, r3)	/* Update TLB entry */
 
 	/* Restore registers */
-#ifdef CONFIG_8xx_CPU6
 	mfspr	r3, SPRN_SPRG_SCRATCH2
-#endif
 	mtspr	SPRN_DAR, r11	/* Tag DAR */
 	EXCEPTION_EPILOG_0
 	rfi
-- 
2.1.0