git.ipfire.org Git - thirdparty/kernel/stable-queue.git/blob

   1 From b253149b843f89cd300cbdbea27ce1f847506f99 Mon Sep 17 00:00:00 2001
   2 From: Len Brown <len.brown@intel.com>
   3 Date: Wed, 15 Jan 2014 00:37:34 -0500
   4 Subject: sched/idle/x86: Restore mwait_idle() to fix boot hangs, to improve power savings and to improve performance
   5
   6 From: Len Brown <len.brown@intel.com>
   7
   8 commit b253149b843f89cd300cbdbea27ce1f847506f99 upstream.
   9
  10 In Linux-3.9 we removed the mwait_idle() loop:
  11
  12   69fb3676df33 ("x86 idle: remove mwait_idle() and "idle=mwait" cmdline param")
  13
  14 The reasoning was that modern machines should be sufficiently
  15 happy during the boot process using the default_idle() HALT
  16 loop, until cpuidle loads and either acpi_idle or intel_idle
  17 invoke the newer MWAIT-with-hints idle loop.
  18
  19 But two machines reported problems:
  20
  21  1. Certain Core2-era machines support MWAIT-C1 and HALT only.
  22     MWAIT-C1 is preferred for optimal power and performance.
  23     But if they support just C1, cpuidle never loads and
  24     so they use the boot-time default idle loop forever.
  25
  26  2. Some laptops will boot-hang if HALT is used,
  27     but will boot successfully if MWAIT is used.
  28     This appears to be a hidden assumption in BIOS SMI,
  29     that is presumably valid on the proprietary OS
  30     where the BIOS was validated.
  31
  32        https://bugzilla.kernel.org/show_bug.cgi?id=60770
  33
  34 So here we effectively revert the patch above, restoring
  35 the mwait_idle() loop.  However, we don't bother restoring
  36 the idle=mwait cmdline parameter, since it appears to add
  37 no value.
  38
  39 Maintainer notes:
  40
  41   For 3.9, simply revert 69fb3676df
  42   for 3.10, patch -F3 applies, fuzz needed due to __cpuinit use in
  43   context For 3.11, 3.12, 3.13, this patch applies cleanly
  44
  45 Tested-by: Mike Galbraith <bitbucket@online.de>
  46 Signed-off-by: Len Brown <len.brown@intel.com>
  47 Acked-by: Mike Galbraith <bitbucket@online.de>
  48 Cc: <stable@vger.kernel.org> # 3.9+
  49 Cc: Borislav Petkov <bp@alien8.de>
  50 Cc: H. Peter Anvin <hpa@zytor.com>
  51 Cc: Ian Malone <ibmalone@gmail.com>
  52 Cc: Josh Boyer <jwboyer@redhat.com>
  53 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  54 Cc: Mike Galbraith <efault@gmx.de>
  55 Cc: Peter Zijlstra <peterz@infradead.org>
  56 Cc: Thomas Gleixner <tglx@linutronix.de>
  57 Link: http://lkml.kernel.org/r/345254a551eb5a6a866e048d7ab570fd2193aca4.1389763084.git.len.brown@intel.com
  58 [ Ported to recent kernels. ]
  59 [ Mike: 3.10 backport ]
  60 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  61 Signed-off-by: Mike Galbraith <efault@gmx.de>
  62 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  63 ---
  64  arch/x86/kernel/process.c |   49 ++++++++++++++++++++++++++++++++++++++++++++++
  65  1 file changed, 49 insertions(+)
  66
  67 --- a/arch/x86/kernel/process.c
  68 +++ b/arch/x86/kernel/process.c
  69 @@ -398,6 +398,52 @@ static void amd_e400_idle(void)
  70                 default_idle();
  71  }
  72
  73 +/*
  74 + * Intel Core2 and older machines prefer MWAIT over HALT for C1.
  75 + * We can't rely on cpuidle installing MWAIT, because it will not load
  76 + * on systems that support only C1 -- so the boot default must be MWAIT.
  77 + *
  78 + * Some AMD machines are the opposite, they depend on using HALT.
  79 + *
  80 + * So for default C1, which is used during boot until cpuidle loads,
  81 + * use MWAIT-C1 on Intel HW that has it, else use HALT.
  82 + */
  83 +static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
  84 +{
  85 +       if (c->x86_vendor != X86_VENDOR_INTEL)
  86 +               return 0;
  87 +
  88 +       if (!cpu_has(c, X86_FEATURE_MWAIT))
  89 +               return 0;
  90 +
  91 +       return 1;
  92 +}
  93 +
  94 +/*
  95 + * MONITOR/MWAIT with no hints, used for default default C1 state.
  96 + * This invokes MWAIT with interrutps enabled and no flags,
  97 + * which is backwards compatible with the original MWAIT implementation.
  98 + */
  99 +
 100 +static void mwait_idle(void)
 101 +{
 102 +       if (!current_set_polling_and_test()) {
 103 +               if (static_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
 104 +                       mb();
 105 +                       clflush((void *)&current_thread_info()->flags);
 106 +                       mb();
 107 +               }
 108 +
 109 +               __monitor((void *)&current_thread_info()->flags, 0, 0);
 110 +               if (!need_resched())
 111 +                       __sti_mwait(0, 0);
 112 +               else
 113 +                       local_irq_enable();
 114 +       } else
 115 +               local_irq_enable();
 116 +       __current_clr_polling();
 117 +}
 118 +
 119  void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 120  {
 121  #ifdef CONFIG_SMP
 122 @@ -411,6 +457,9 @@ void __cpuinit select_idle_routine(const
 123                 /* E400: APIC timer interrupt does not wake up CPU from C1e */
 124                 pr_info("using AMD E400 aware idle routine\n");
 125                 x86_idle = amd_e400_idle;
 126 +       } else if (prefer_mwait_c1_over_halt(c)) {
 127 +               pr_info("using mwait in idle threads\n");
 128 +               x86_idle = mwait_idle;
 129         } else
 130                 x86_idle = default_idle;
 131  }