[PATCH] powerpc/pseries: Use H_CLEAR_HPT to clear MMU hash table during kexec

From: Anton Blanchard <redacted>

An hcall was recently added that does exactly what we need
during kexec - it clears the entire MMU hash table, ignoring any
VRMA mappings.

Try it and fall back to the old method if we get a failure.

On a POWER8 box with 5TB of memory, this reduces the time it takes to
kexec a new kernel from from 4 minutes to 1 minute.

Signed-off-by: Anton Blanchard <redacted>
---
 arch/powerpc/include/asm/hvcall.h     |  3 ++-
 arch/powerpc/platforms/pseries/lpar.c | 14 +++++++++++++-
 2 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
index 708edeb..489748e 100644
--- a/arch/powerpc/include/asm/hvcall.h
+++ b/arch/powerpc/include/asm/hvcall.h

@@ -275,7 +275,8 @@
 #define H_COP			0x304
 #define H_GET_MPP_X		0x314
 #define H_SET_MODE		0x31C
-#define MAX_HCALL_OPCODE	H_SET_MODE
+#define H_CLEAR_HPT		0x358
+#define MAX_HCALL_OPCODE	H_CLEAR_HPT
 
 /* H_VIOCTL functions */
 #define H_GET_VIOA_DUMP_SIZE	0x01

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 86707e6..03884a8 100644
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c

@@ -221,7 +221,7 @@ static long pSeries_lpar_hpte_remove(unsigned long hpte_group)
 	return -1;
 }
 
-static void pSeries_lpar_hptab_clear(void)
+static void __pSeries_lpar_clear_hpt(void)
 {
 	unsigned long size_bytes = 1UL << ppc64_pft_size;
 	unsigned long hpte_count = size_bytes >> 4;

@@ -249,6 +249,18 @@ static void pSeries_lpar_hptab_clear(void)
 					&(ptes[j].pteh), &(ptes[j].ptel));
 		}
 	}
+}
+
+static void pSeries_lpar_hptab_clear(void)
+{
+	int rc;
+
+	do {
+		rc = plpar_hcall_norets(H_CLEAR_HPT);
+	} while (rc == H_CONTINUE);
+
+	if (rc != H_SUCCESS)
+		__pSeries_lpar_clear_hpt();
 
 #ifdef __LITTLE_ENDIAN__
 	/*

-- 
2.7.4

On 10/01/2016 04:11 PM, Anton Blanchard wrote:

From: Anton Blanchard <redacted>

An hcall was recently added that does exactly what we need
during kexec - it clears the entire MMU hash table, ignoring any
VRMA mappings.

Try it and fall back to the old method if we get a failure.

On a POWER8 box with 5TB of memory, this reduces the time it takes to
kexec a new kernel from from 4 minutes to 1 minute.

Signed-off-by: Anton Blanchard <redacted>

Tested-by: Mahesh Salgaonkar <redacted>

On Sat, 2016-01-10 at 10:41:56 UTC, Anton Blanchard wrote:

From: Anton Blanchard <redacted>

An hcall was recently added that does exactly what we need
during kexec - it clears the entire MMU hash table, ignoring any
VRMA mappings.

Try it and fall back to the old method if we get a failure.

On a POWER8 box with 5TB of memory, this reduces the time it takes to
kexec a new kernel from from 4 minutes to 1 minute.

Signed-off-by: Anton Blanchard <redacted>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/5246adec59458b5d325b8e1462ea9e

cheers