From: Len Brown <len.brown@xxxxxxxxx> Linux 3.10 changed the timing of how thread_info->flags is touched: x86: Use generic idle loop (7d1a941731fabf27e5fb6edbebb79fe856edb4e5) This caused Intel NHM-EX and WSM-EX servers to experience a large number of immediate MONITOR/MWAIT break wakeups, which caused cpuidle to demote from deep C-states to shallow C-states, which caused these platforms to experience a significant increase in idle power. Note that this issue was already present before the commit above, however, it wasn't seen often enough to be noticed in power measurements. Here we extend an errata workaround from the Core2 EX "Dunnington" to extend to NHM-EX and WSM-EX, to prevent these immediate returns from MWAIT, reducing idle power on these platforms. While only acpi_idle ran on Dunnington, intel_idle may also run on these two newer systems. As of today, there are no other models that are known to need this tweak. ref: https://lkml.org/lkml/2013/12/7/22 Signed-off-by: Len Brown <len.brown@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 3.12.x, 3.11.x, 3.10.x --- arch/x86/kernel/cpu/intel.c | 3 ++- drivers/idle/intel_idle.c | 3 +++ 2 files changed, 5 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index dc1ec0d..ea04b34 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -387,7 +387,8 @@ static void init_intel(struct cpuinfo_x86 *c) set_cpu_cap(c, X86_FEATURE_PEBS); } - if (c->x86 == 6 && c->x86_model == 29 && cpu_has_clflush) + if (c->x86 == 6 && cpu_has_clflush && + (c->x86_model == 29 || c->x86_model == 46 || c->x86_model == 47)) set_cpu_cap(c, X86_FEATURE_CLFLUSH_MONITOR); #ifdef CONFIG_X86_64 diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c index 92d1206..f80b700 100644 --- a/drivers/idle/intel_idle.c +++ b/drivers/idle/intel_idle.c @@ -377,6 +377,9 @@ static int intel_idle(struct cpuidle_device *dev, if (!current_set_polling_and_test()) { + if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) + clflush((void *)¤t_thread_info()->flags); + __monitor((void *)¤t_thread_info()->flags, 0, 0); smp_mb(); if (!need_resched()) -- 1.8.5.1.19.gdaad3aa -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html