Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2993369AbbEPIpn (ORCPT ); Sat, 16 May 2015 04:45:43 -0400 Received: from bband-dyn183.178-41-215.t-com.sk ([178.41.215.183]:22478 "EHLO ip4-83-240-18-248.cust.nbox.cz" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1946423AbbEPIFr (ORCPT ); Sat, 16 May 2015 04:05:47 -0400 From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Len Brown , Borislav Petkov , "H. Peter Anvin" , Ian Malone , Josh Boyer , Linus Torvalds , Mike Galbraith , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Jiri Slaby Subject: [PATCH 3.12 010/142] sched/idle/x86: Restore mwait_idle() to fix boot hangs, to improve power savings and to improve performance Date: Sat, 16 May 2015 09:36:10 +0200 Message-Id: <257ccf0a22d82dd694bc77d8b8fd151f724d6856.1431761807.git.jslaby@suse.cz> X-Mailer: git-send-email 2.3.7 In-Reply-To: <70c3d4ae1322b9e9bd7443ef574af5635234a0fa.1431761807.git.jslaby@suse.cz> References: <70c3d4ae1322b9e9bd7443ef574af5635234a0fa.1431761807.git.jslaby@suse.cz> In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4595 Lines: 140 From: Len Brown 3.12-stable review patch. If anyone has any objections, please let me know. =============== 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: # 3.9+ 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. ] [ Mike: 3.10 backport ] Signed-off-by: Ingo Molnar Signed-off-by: Mike Galbraith Signed-off-by: Jiri Slaby --- arch/x86/kernel/process.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 3fb8d95ab8b5..c5db2a43e730 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -398,6 +398,52 @@ 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 (!current_set_polling_and_test()) { + if (static_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) { + mb(); + clflush((void *)¤t_thread_info()->flags); + mb(); + } + + __monitor((void *)¤t_thread_info()->flags, 0, 0); + if (!need_resched()) + __sti_mwait(0, 0); + else + local_irq_enable(); + } else + local_irq_enable(); + __current_clr_polling(); +} + void select_idle_routine(const struct cpuinfo_x86 *c) { #ifdef CONFIG_SMP @@ -411,6 +457,9 @@ void select_idle_routine(const struct cpuinfo_x86 *c) /* 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; } -- 2.3.7 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/