Messages in this thread | | | Date | Thu, 2 Jun 2022 21:11:45 +0530 | Subject | Re: [PATCH v4 1/3] x86: Handle idle=nomwait cmdline properly for x86_idle | From | Wyes Karny <> |
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Hi Rui,
On 5/25/2022 1:36 PM, Zhang Rui wrote: > On Mon, 2022-05-23 at 22:25 +0530, Wyes Karny wrote: >> When kernel is booted with idle=nomwait do not use MWAIT as the >> default idle state. >> >> If the user boots the kernel with idle=nomwait, it is a clear >> direction to not use mwait as the default idle state. >> However, the current code does not take this into consideration >> while selecting the default idle state on x86. >> >> This patch fixes it by checking for the idle=nomwait boot option in >> prefer_mwait_c1_over_halt(). >> >> Also update the documentation around idle=nomwait appropriately. >> >> Signed-off-by: Wyes Karny <wyes.karny@amd.com> >> --- >> Changes in v4: >> - Update documentation around idle=nomwait >> - Rename patch subject >> >> Documentation/admin-guide/pm/cpuidle.rst | 15 +++++++++------ >> arch/x86/kernel/process.c | 6 +++++- >> 2 files changed, 14 insertions(+), 7 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..4e0178b066c5 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; >> >> @@ -932,7 +936,7 @@ 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 >> + * it means that mwait will be disabled for CPU >> C1/C2/C3 >> * states. In such case it won't touch the variable >> * of boot_option_idle_override. > > the code didn't change boot_option_idle_override when it was > introduced, but this has changed since commit d18960494f65 ("ACPI, > intel_idle: Cleanup idle= internal variables")
Could you please clarify bit more why the commit you mentioned is related to this patch?
> > thanks, > rui >
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