Messages in this thread Patch in this message | | | Subject | Re: [PATCH v3 1/3] x86: Use HLT in default_idle when idle=nomwait cmdline arg is passed | From | Zhang Rui <> | Date | Fri, 20 May 2022 23:38:17 +0800 |
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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.
} 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; >
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