Messages in this thread | | | Date | Mon, 23 May 2022 10:32:48 +0530 | Subject | Re: [PATCH v3 1/3] x86: Use HLT in default_idle when idle=nomwait cmdline arg is passed | From | Wyes Karny <> |
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Hello Rui,
On 5/20/2022 9:08 PM, Zhang Rui wrote: > Hi, Wyes, > > On Tue, 2022-05-10 at 15:48 +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. > > I think we also need to update the comment in idle_setup() as well.
Agreed. Will update. Thanks!
> > } 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. > */ > boot_op > tion_idle_override = IDLE_NOMWAIT; > } else > > thanks, > rui >> >> Signed-off-by: Wyes Karny <wyes.karny@amd.com> >> --- >> Changes in v3: >> - Update documentation around idle=mwait >> >> Documentation/admin-guide/pm/cpuidle.rst | 15 +++++++++------ >> arch/x86/kernel/process.c | 4 ++++ >> 2 files changed, 13 insertions(+), 6 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..49b915d1b7b4 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; >> >
Thanks, Wyes
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