diff options
| -rw-r--r-- | Documentation/admin-guide/pm/cpuidle.rst | 15 | ||||
| -rw-r--r-- | arch/x86/kernel/process.c | 9 |
2 files changed, 15 insertions, 9 deletions
diff --git a/Documentation/admin-guide/pm/cpuidle.rst b/Documentation/admin-guide/pm/cpuidle.rst index aec2cd2aaea7..19754beb5a4e 100644 --- a/Documentation/admin-guide/pm/cpuidle.rst +++ b/Documentation/admin-guide/pm/cpuidle.rst @@ -612,8 +612,8 @@ the ``menu`` governor to be used on the systems that use the ``ladder`` governor by default this way, for example. The other kernel command line parameters controlling CPU idle time management -described below are only relevant for the *x86* architecture and some of -them affect Intel processors only. +described below are only relevant for the *x86* architecture and references +to ``intel_idle`` affect Intel processors only. The *x86* architecture support code recognizes three kernel command line options related to CPU idle time management: ``idle=poll``, ``idle=halt``, @@ -635,10 +635,13 @@ idle, so it very well may hurt single-thread computations performance as well as energy-efficiency. Thus using it for performance reasons may not be a good idea at all.] -The ``idle=nomwait`` option disables the ``intel_idle`` driver and causes -``acpi_idle`` to be used (as long as all of the information needed by it is -there in the system's ACPI tables), but it is not allowed to use the -``MWAIT`` instruction of the CPUs to ask the hardware to enter idle states. +The ``idle=nomwait`` option prevents the use of ``MWAIT`` instruction of +the CPU to enter idle states. When this option is used, the ``acpi_idle`` +driver will use the ``HLT`` instruction instead of ``MWAIT``. On systems +running Intel processors, this option disables the ``intel_idle`` driver +and forces the use of the ``acpi_idle`` driver instead. Note that in either +case, ``acpi_idle`` driver will function only if all the information needed +by it is in the system's ACPI tables. In addition to the architecture-level kernel command line options affecting CPU idle time management, there are parameters affecting individual ``CPUIdle`` diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index b370767f5b19..dca2e5e2fae2 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -824,6 +824,10 @@ static void amd_e400_idle(void) */ static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c) { + /* User has disallowed the use of MWAIT. Fallback to HALT */ + if (boot_option_idle_override == IDLE_NOMWAIT) + return 0; + if (c->x86_vendor != X86_VENDOR_INTEL) return 0; @@ -932,9 +936,8 @@ static int __init idle_setup(char *str) } else if (!strcmp(str, "nomwait")) { /* * If the boot option of "idle=nomwait" is added, - * it means that mwait will be disabled for CPU C2/C3 - * states. In such case it won't touch the variable - * of boot_option_idle_override. + * it means that mwait will be disabled for CPU C1/C2/C3 + * states. */ boot_option_idle_override = IDLE_NOMWAIT; } else |