x86 idle: remove mwait_idle() and "idle=mwait" cmdline param

mwait_idle() is a C1-only idle loop intended to be more efficient
than HLT, starting on Pentium-4 HT-enabled processors.

But mwait_idle() has been replaced by the more general
mwait_idle_with_hints(), which handles both C1 and deeper C-states.
ACPI processor_idle and intel_idle use only mwait_idle_with_hints(),
and no longer use mwait_idle().

Here we simplify the x86 native idle code by removing mwait_idle(),
and the "idle=mwait" bootparam used to invoke it.

Since Linux 3.0 there has been a boot-time warning when "idle=mwait"
was invoked saying it would be removed in 2012.  This removal
was also noted in the (now removed:-) feature-removal-schedule.txt.

After this change, kernels configured with
(CONFIG_ACPI=n && CONFIG_INTEL_IDLE=n) when run on hardware
that supports MWAIT will simply use HLT.  If MWAIT is desired
on those systems, cpuidle and the cpuidle drivers above
can be enabled.

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org

1 files changed, 1 insertions, 78 deletions

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 7ed9f6b08ba0..cd5a4c9ef835 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -421,27 +421,6 @@ void stop_this_cpu(void *dummy)
         }
 }
 
-/* Default MONITOR/MWAIT with no hints, used for default C1 state */
-static void mwait_idle(void)
-{
-        if (!need_resched()) {
-                trace_power_start_rcuidle(POWER_CSTATE, 1, smp_processor_id());
-                trace_cpu_idle_rcuidle(1, smp_processor_id());
-                if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
-                        clflush((void *)&current_thread_info()->flags);
-
-                __monitor((void *)&current_thread_info()->flags, 0, 0);
-                smp_mb();
-                if (!need_resched())
-                        __sti_mwait(0, 0);
-                else
-                        local_irq_enable();
-                trace_power_end_rcuidle(smp_processor_id());
-                trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
-        } else
-                local_irq_enable();
-}
-
 /*
  * On SMP it's slightly faster (but much more power-consuming!)
  * to poll the ->work.need_resched flag instead of waiting for the
@@ -458,53 +437,6 @@ static void poll_idle(void)
         trace_cpu_idle_rcuidle(PWR_EVENT_EXIT, smp_processor_id());
 }
 
-/*
- * mwait selection logic:
- *
- * It depends on the CPU. For AMD CPUs that support MWAIT this is
- * wrong. Family 0x10 and 0x11 CPUs will enter C1 on HLT. Powersavings
- * then depend on a clock divisor and current Pstate of the core. If
- * all cores of a processor are in halt state (C1) the processor can
- * enter the C1E (C1 enhanced) state. If mwait is used this will never
- * happen.
- *
- * idle=mwait overrides this decision and forces the usage of mwait.
- */
-
-#define MWAIT_INFO                      0x05
-#define MWAIT_ECX_EXTENDED_INFO         0x01
-#define MWAIT_EDX_C1                    0xf0
-
-int mwait_usable(const struct cpuinfo_x86 *c)
-{
-        u32 eax, ebx, ecx, edx;
-
-        /* Use mwait if idle=mwait boot option is given */
-        if (boot_option_idle_override == IDLE_FORCE_MWAIT)
-                return 1;
-
-        /*
-         * Any idle= boot option other than idle=mwait means that we must not
-         * use mwait. Eg: idle=halt or idle=poll or idle=nomwait
-         */
-        if (boot_option_idle_override != IDLE_NO_OVERRIDE)
-                return 0;
-
-        if (c->cpuid_level < MWAIT_INFO)
-                return 0;
-
-        cpuid(MWAIT_INFO, &eax, &ebx, &ecx, &edx);
-        /* Check, whether EDX has extended info about MWAIT */
-        if (!(ecx & MWAIT_ECX_EXTENDED_INFO))
-                return 1;
-
-        /*
-         * edx enumeratios MONITOR/MWAIT extensions. Check, whether
-         * C1  supports MWAIT
-         */
-        return (edx & MWAIT_EDX_C1);
-}
-
 bool amd_e400_c1e_detected;
 EXPORT_SYMBOL(amd_e400_c1e_detected);
 
@@ -576,13 +508,7 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
         if (pm_idle)
                 return;
 
-        if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
-                /*
-                 * One CPU supports mwait => All CPUs supports mwait
-                 */
-                pr_info("using mwait in idle threads\n");
-                pm_idle = mwait_idle;
-        } else if (cpu_has_amd_erratum(amd_erratum_400)) {
+        if (cpu_has_amd_erratum(amd_erratum_400)) {
                 /* E400: APIC timer interrupt does not wake up CPU from C1e */
                 pr_info("using AMD E400 aware idle routine\n");
                 pm_idle = amd_e400_idle;
@@ -606,9 +532,6 @@ static int __init idle_setup(char *str)
                 pr_info("using polling idle threads\n");
                 pm_idle = poll_idle;
                 boot_option_idle_override = IDLE_POLL;
-        } else if (!strcmp(str, "mwait")) {
-                boot_option_idle_override = IDLE_FORCE_MWAIT;
-                WARN_ONCE(1, "\"idle=mwait\" will be removed in 2012\n");
         } else if (!strcmp(str, "halt")) {
                 /*
                  * When the boot option of idle=halt is added, halt is