From 76cbd8a8f8b0dddbff89a6708bd5bd13c0d21a00 Mon Sep 17 00:00:00 2001 From: Michael Neuling Date: Tue, 8 Jun 2010 14:57:02 +1000 Subject: [PATCH] powerpc: Enable asymmetric SMT scheduling on POWER7 The POWER7 core has dynamic SMT mode switching which is controlled by the hypervisor. There are 3 SMT modes: SMT1 uses thread 0 SMT2 uses threads 0 & 1 SMT4 uses threads 0, 1, 2 & 3 When in any particular SMT mode, all threads have the same performance as each other (ie. at any moment in time, all threads perform the same). The SMT mode switching works such that when linux has threads 2 & 3 idle and 0 & 1 active, it will cede (H_CEDE hypercall) threads 2 and 3 in the idle loop and the hypervisor will automatically switch to SMT2 for that core (independent of other cores). The opposite is not true, so if threads 0 & 1 are idle and 2 & 3 are active, we will stay in SMT4 mode. Similarly if thread 0 is active and threads 1, 2 & 3 are idle, we'll go into SMT1 mode. If we can get the core into a lower SMT mode (SMT1 is best), the threads will perform better (since they share less core resources). Hence when we have idle threads, we want them to be the higher ones. This adds a feature bit for asymmetric packing to powerpc and then enables it on POWER7. Signed-off-by: Michael Neuling Signed-off-by: Peter Zijlstra Acked-by: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: linuxppc-dev@ozlabs.org LKML-Reference: <20100608045702.31FB5CC8C7@localhost.localdomain> Signed-off-by: Ingo Molnar --- arch/powerpc/include/asm/cputable.h | 3 ++- arch/powerpc/kernel/process.c | 9 +++++++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h index b0b21134f61a..4b611ca1a768 100644 --- a/arch/powerpc/include/asm/cputable.h +++ b/arch/powerpc/include/asm/cputable.h @@ -197,6 +197,7 @@ extern const char *powerpc_base_platform; #define CPU_FTR_SAO LONG_ASM_CONST(0x0020000000000000) #define CPU_FTR_CP_USE_DCBTZ LONG_ASM_CONST(0x0040000000000000) #define CPU_FTR_UNALIGNED_LD_STD LONG_ASM_CONST(0x0080000000000000) +#define CPU_FTR_ASYM_SMT LONG_ASM_CONST(0x0100000000000000) #ifndef __ASSEMBLY__ @@ -412,7 +413,7 @@ extern const char *powerpc_base_platform; CPU_FTR_MMCRA | CPU_FTR_SMT | \ CPU_FTR_COHERENT_ICACHE | CPU_FTR_LOCKLESS_TLBIE | \ CPU_FTR_PURR | CPU_FTR_SPURR | CPU_FTR_REAL_LE | \ - CPU_FTR_DSCR | CPU_FTR_SAO) + CPU_FTR_DSCR | CPU_FTR_SAO | CPU_FTR_ASYM_SMT) #define CPU_FTRS_CELL (CPU_FTR_USE_TB | CPU_FTR_LWSYNC | \ CPU_FTR_PPCAS_ARCH_V2 | CPU_FTR_CTRL | \ CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \ diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c index 9d255b4f0a0e..a3f347c635b2 100644 --- a/arch/powerpc/kernel/process.c +++ b/arch/powerpc/kernel/process.c @@ -1268,3 +1268,12 @@ unsigned long randomize_et_dyn(unsigned long base) return ret; } + +int arch_sd_sibiling_asym_packing(void) +{ + if (cpu_has_feature(CPU_FTR_ASYM_SMT)) { + printk_once(KERN_INFO "Enabling Asymmetric SMT scheduling\n"); + return SD_ASYM_PACKING; + } + return 0; +} -- GitLab