From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:44901 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1423039AbbD2MME (ORCPT ); Wed, 29 Apr 2015 08:12:04 -0400 Subject: Patch "sched/idle/x86: Restore mwait_idle() to fix boot hangs, to improve power savings and to improve performance" has been added to the 3.19-stable tree To: len.brown@intel.com, bitbucket@online.de, bp@alien8.de, efault@gmx.de, gregkh@linuxfoundation.org, hpa@zytor.com, ibmalone@gmail.com, jwboyer@redhat.com, mingo@kernel.org, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org Cc: , From: Date: Wed, 29 Apr 2015 14:11:57 +0200 Message-ID: <143030951795189@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled sched/idle/x86: Restore mwait_idle() to fix boot hangs, to improve power savings and to improve performance to the 3.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-idle-x86-restore-mwait_idle-to-fix-boot-hangs-to-improve-power-savings-and-to-improve-performance.patch and it can be found in the queue-3.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From b253149b843f89cd300cbdbea27ce1f847506f99 Mon Sep 17 00:00:00 2001 From: Len Brown Date: Wed, 15 Jan 2014 00:37:34 -0500 Subject: sched/idle/x86: Restore mwait_idle() to fix boot hangs, to improve power savings and to improve performance From: Len Brown commit b253149b843f89cd300cbdbea27ce1f847506f99 upstream. In Linux-3.9 we removed the mwait_idle() loop: 69fb3676df33 ("x86 idle: remove mwait_idle() and "idle=mwait" cmdline param") The reasoning was that modern machines should be sufficiently happy during the boot process using the default_idle() HALT loop, until cpuidle loads and either acpi_idle or intel_idle invoke the newer MWAIT-with-hints idle loop. But two machines reported problems: 1. Certain Core2-era machines support MWAIT-C1 and HALT only. MWAIT-C1 is preferred for optimal power and performance. But if they support just C1, cpuidle never loads and so they use the boot-time default idle loop forever. 2. Some laptops will boot-hang if HALT is used, but will boot successfully if MWAIT is used. This appears to be a hidden assumption in BIOS SMI, that is presumably valid on the proprietary OS where the BIOS was validated. https://bugzilla.kernel.org/show_bug.cgi?id=60770 So here we effectively revert the patch above, restoring the mwait_idle() loop. However, we don't bother restoring the idle=mwait cmdline parameter, since it appears to add no value. Maintainer notes: For 3.9, simply revert 69fb3676df for 3.10, patch -F3 applies, fuzz needed due to __cpuinit use in context For 3.11, 3.12, 3.13, this patch applies cleanly Tested-by: Mike Galbraith Signed-off-by: Len Brown Acked-by: Mike Galbraith Cc: Borislav Petkov Cc: H. Peter Anvin Cc: Ian Malone Cc: Josh Boyer Cc: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/345254a551eb5a6a866e048d7ab570fd2193aca4.1389763084.git.len.brown@intel.com [ Ported to recent kernels. ] Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/mwait.h | 8 +++++++ arch/x86/kernel/process.c | 47 +++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+) --- a/arch/x86/include/asm/mwait.h +++ b/arch/x86/include/asm/mwait.h @@ -30,6 +30,14 @@ static inline void __mwait(unsigned long :: "a" (eax), "c" (ecx)); } +static inline void __sti_mwait(unsigned long eax, unsigned long ecx) +{ + trace_hardirqs_on(); + /* "mwait %eax, %ecx;" */ + asm volatile("sti; .byte 0x0f, 0x01, 0xc9;" + :: "a" (eax), "c" (ecx)); +} + /* * This uses new MONITOR/MWAIT instructions on P4 processors with PNI, * which can obviate IPI to trigger checking of need_resched. --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -24,6 +24,7 @@ #include #include #include +#include #include #include #include @@ -398,6 +399,49 @@ static void amd_e400_idle(void) default_idle(); } +/* + * Intel Core2 and older machines prefer MWAIT over HALT for C1. + * We can't rely on cpuidle installing MWAIT, because it will not load + * on systems that support only C1 -- so the boot default must be MWAIT. + * + * Some AMD machines are the opposite, they depend on using HALT. + * + * So for default C1, which is used during boot until cpuidle loads, + * use MWAIT-C1 on Intel HW that has it, else use HALT. + */ +static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c) +{ + if (c->x86_vendor != X86_VENDOR_INTEL) + return 0; + + if (!cpu_has(c, X86_FEATURE_MWAIT)) + return 0; + + return 1; +} + +/* + * MONITOR/MWAIT with no hints, used for default default C1 state. + * This invokes MWAIT with interrutps enabled and no flags, + * which is backwards compatible with the original MWAIT implementation. + */ + +static void mwait_idle(void) +{ + if (!need_resched()) { + if (this_cpu_has(X86_BUG_CLFLUSH_MONITOR)) + clflush((void *)¤t_thread_info()->flags); + + __monitor((void *)¤t_thread_info()->flags, 0, 0); + smp_mb(); + if (!need_resched()) + __sti_mwait(0, 0); + else + local_irq_enable(); + } else + local_irq_enable(); +} + void select_idle_routine(const struct cpuinfo_x86 *c) { #ifdef CONFIG_SMP @@ -411,6 +455,9 @@ void select_idle_routine(const struct cp /* E400: APIC timer interrupt does not wake up CPU from C1e */ pr_info("using AMD E400 aware idle routine\n"); x86_idle = amd_e400_idle; + } else if (prefer_mwait_c1_over_halt(c)) { + pr_info("using mwait in idle threads\n"); + x86_idle = mwait_idle; } else x86_idle = default_idle; } Patches currently in stable-queue which might be from len.brown@intel.com are queue-3.19/sched-idle-x86-optimize-unnecessary-mwait_idle-resched-ipis.patch queue-3.19/sched-idle-x86-restore-mwait_idle-to-fix-boot-hangs-to-improve-power-savings-and-to-improve-performance.patch