From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754041Ab3LSOlx (ORCPT ); Thu, 19 Dec 2013 09:41:53 -0500 Received: from terminus.zytor.com ([198.137.202.10]:60421 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753926Ab3LSOlv (ORCPT ); Thu, 19 Dec 2013 09:41:51 -0500 User-Agent: K-9 Mail for Android In-Reply-To: <20131219122257.GC11279@gmail.com> References: <20131219122257.GC11279@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [PATCH] x86 idle: repair large-server 50-watt idle-power regression From: "H. Peter Anvin" Date: Thu, 19 Dec 2013 06:40:41 -0800 To: Ingo Molnar , Len Brown CC: x86@kernel.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Len Brown , stable@vger.kernel.org, Linus Torvalds , Thomas Gleixner , Peter Zijlstra , Mike Galbraith , Borislav Petkov Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ... or just use static_cpu_has() maybe? Ingo Molnar wrote: > >* Len Brown wrote: > >> From: Len Brown >> >> 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 >> Cc: # 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); > >I don't think either of these casts to '(void *)' is needed, both the >clflush() and __monitor() will take pointers. > >Looks good to me otherwise - except that maybe the best way to >represent this quirk would be for the CLFLUSH+MONITOR sequence to be a >single 'instruction' which is patched in dynamically during bootup, >using our usual alternatives framework. > >On non-affected CPUs a NOP would remain in place of the CLFLUSH, >eliminating the branch above. > >So the whole thing could be thought of as a slightly more complex >'monitor' instruction - not exposing the quirk details to actual usage >sites. > >Thanks, > > Ingo -- Sent from my mobile phone. Please pardon brevity and lack of formatting.