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- Remove the vendor check when selecting MWAIT as the default idle state

Browse Source 
- Respect idle=nomwait when supplied on the kernel cmdline
 
 - Two small cleanups
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Merge tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 cpu updates from Borislav Petkov:

 - Remove the vendor check when selecting MWAIT as the default idle
   state

 - Respect idle=nomwait when supplied on the kernel cmdline

 - Two small cleanups

* tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/cpu: Use MSR_IA32_MISC_ENABLE constants
  x86: Fix comment for X86_FEATURE_ZEN
  x86: Remove vendor checks from prefer_mwait_c1_over_halt
  x86: Handle idle=nomwait cmdline properly for x86_idle
This commit is contained in:
Linus Torvalds 2022-08-01 09:49:29 -07:00
commit 42efa5e3a8
5 changed files with 44 additions and 22 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
Documentation/admin-guide/pm/cpuidle.rst
View File

@ -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``

2
arch/x86/include/asm/cpufeatures.h
View File

@ -219,7 +219,7 @@
#define X86_FEATURE_IBRS ( 7*32+25) /* Indirect Branch Restricted Speculation */
#define X86_FEATURE_IBPB ( 7*32+26) /* Indirect Branch Prediction Barrier */
#define X86_FEATURE_STIBP ( 7*32+27) /* Single Thread Indirect Branch Predictors */
#define X86_FEATURE_ZEN ( 7*32+28) /* "" CPU is AMD family 0x17 or above (Zen) */
#define X86_FEATURE_ZEN (7*32+28) /* "" CPU based on Zen microarchitecture */
#define X86_FEATURE_L1TF_PTEINV ( 7*32+29) /* "" L1TF workaround PTE inversion */
#define X86_FEATURE_IBRS_ENHANCED ( 7*32+30) /* Enhanced IBRS */
#define X86_FEATURE_MSR_IA32_FEAT_CTL ( 7*32+31) /* "" MSR IA32_FEAT_CTL configured */

1
arch/x86/include/asm/mwait.h
View File

@ -13,6 +13,7 @@
#define MWAIT_SUBSTATE_SIZE 4
#define MWAIT_HINT2CSTATE(hint) (((hint) >> MWAIT_SUBSTATE_SIZE) & MWAIT_CSTATE_MASK)
#define MWAIT_HINT2SUBSTATE(hint) ((hint) & MWAIT_CSTATE_MASK)
#define MWAIT_C1_SUBSTATE_MASK 0xf0
#define CPUID_MWAIT_LEAF 5
#define CPUID5_ECX_EXTENSIONS_SUPPORTED 0x1

4
arch/x86/kernel/cpu/intel.c
View File

@ -682,9 +682,9 @@ static void init_intel(struct cpuinfo_x86 *c)
unsigned int l1, l2;
rdmsr(MSR_IA32_MISC_ENABLE, l1, l2);
if (!(l1 & (1<<11)))
if (!(l1 & MSR_IA32_MISC_ENABLE_BTS_UNAVAIL))
set_cpu_cap(c, X86_FEATURE_BTS);
if (!(l1 & (1<<12)))
if (!(l1 & MSR_IA32_MISC_ENABLE_PEBS_UNAVAIL))
set_cpu_cap(c, X86_FEATURE_PEBS);
}

44
arch/x86/kernel/process.c
View File

@ -810,24 +810,43 @@ static void amd_e400_idle(void)
}
/*
* 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.
* Prefer MWAIT over HALT if MWAIT is supported, MWAIT_CPUID leaf
* exists and whenever MONITOR/MWAIT extensions are present there is at
* least one C1 substate.
*
* 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.
* Do not prefer MWAIT if MONITOR instruction has a bug or idle=nomwait
* is passed to kernel commandline parameter.
*/
static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
{
if (c->x86_vendor != X86_VENDOR_INTEL)
u32 eax, ebx, ecx, edx;
/* User has disallowed the use of MWAIT. Fallback to HALT */
if (boot_option_idle_override == IDLE_NOMWAIT)
return 0;
if (!cpu_has(c, X86_FEATURE_MWAIT) || boot_cpu_has_bug(X86_BUG_MONITOR))
/* MWAIT is not supported on this platform. Fallback to HALT */
if (!cpu_has(c, X86_FEATURE_MWAIT))
return 0;
return 1;
/* Monitor has a bug. Fallback to HALT */
if (boot_cpu_has_bug(X86_BUG_MONITOR))
return 0;
cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
/*
* If MWAIT extensions are not available, it is safe to use MWAIT
* with EAX=0, ECX=0.
*/
if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED))
return 1;
/*
* If MWAIT extensions are available, there should be at least one
* MWAIT C1 substate present.
*/
return (edx & MWAIT_C1_SUBSTATE_MASK);
}
/*
@ -932,9 +951,8 @@ 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