Re: [PATCH -V3 11/11] arch/powerpc: Add 64TB support
From: Aneesh Kumar K.V <hidden>
Date: 2012-07-23 08:49:41
Paul Mackerras [off-list ref] writes:
On Mon, Jul 09, 2012 at 06:43:41PM +0530, Aneesh Kumar K.V wrote:quoted
From: "Aneesh Kumar K.V" <redacted> Increase max addressable range to 64TB. This is not tested on real hardware yet. Signed-off-by: Aneesh Kumar K.V <redacted> --- arch/powerpc/include/asm/mmu-hash64.h | 8 ++++---- arch/powerpc/include/asm/pgtable-ppc64-4k.h | 2 +- arch/powerpc/include/asm/pgtable-ppc64-64k.h | 2 +- arch/powerpc/include/asm/processor.h | 4 ++-- arch/powerpc/include/asm/sparsemem.h | 4 ++-- 5 files changed, 10 insertions(+), 10 deletions(-)diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h index aa0d560..a227ba7 100644 --- a/arch/powerpc/include/asm/mmu-hash64.h +++ b/arch/powerpc/include/asm/mmu-hash64.h@@ -374,16 +374,16 @@ extern void slb_set_size(u16 size); */ #define VSID_MULTIPLIER_256M ASM_CONST(200730139) /* 28-bit prime */ -#define VSID_BITS_256M 36 +#define VSID_BITS_256M 38 #define VSID_MODULUS_256M ((1UL<<VSID_BITS_256M)-1)With these settings, the multiplication in ASM_VSID_SCRAMBLE could overflow, leading to incorrect results (which would cause occasional corruption of user processes under heavy load). You will need to reduce the multiplier to be less than 2^26, and it will need to be co-prime with 2^38 - 1. (Probably, the same value as we use in the 1T case would be OK.)
I ended up using the same value as VSID_MULTIPLIER_1T. (gdb) p/d 1ull << 38 $1 = 274877906944 (gdb) p/d 274877906943/12538073 $2 = 21923 (gdb) p/d 12538073ll*21923 $5 = 274872174379