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intel_idle: add 'preferred_cstates' module argument

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On Sapphire Rapids Xeon (SPR) the C1 and C1E states are basically mutually
exclusive - only one of them can be enabled. By default, 'intel_idle' driver
enables C1 and disables C1E. However, some users prefer to use C1E instead of
C1, because it saves more energy.

This patch adds a new module parameter ('preferred_cstates') for enabling C1E
and disabling C1. Here is the idea behind it.

1. This option has effect only for "mutually exclusive" C-states like C1 and
   C1E on SPR.
2. It does not have any effect on independent C-states, which do not require
   other C-states to be disabled (most states on most platforms as of today).
3. For mutually exclusive C-states, the 'intel_idle' driver always has a
   reasonable default, such as enabling C1 on SPR by default. On other
   platforms, the default may be different.
4. Users can override the default using the 'preferred_cstates' parameter.
5. The parameter accepts the preferred C-states bit-mask, similarly to the
   existing 'states_off' parameter.
6. This parameter is not limited to C1/C1E, and leaves room for supporting
   other mutually exclusive C-states, if they come in the future.

Today 'intel_idle' can only be compiled-in, which means that on SPR, in order
to disable C1 and enable C1E, users should boot with the following kernel
argument: intel_idle.preferred_cstates=4

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Artem Bityutskiy 2022-03-02 10:15:59 +02:00 committed by Rafael J. Wysocki
parent 9edf3c0ffe
commit da0e58c038
1 changed files with 46 additions and 0 deletions
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46
drivers/idle/intel_idle.c
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@ -64,6 +64,7 @@ static struct cpuidle_driver intel_idle_driver = {
/* intel_idle.max_cstate=0 disables driver */
static int max_cstate = CPUIDLE_STATE_MAX - 1;
static unsigned int disabled_states_mask;
static unsigned int preferred_states_mask;
static struct cpuidle_device __percpu *intel_idle_cpuidle_devices;
@ -1400,6 +1401,8 @@ static inline void intel_idle_init_cstates_acpi(struct cpuidle_driver *drv) { }
static inline bool intel_idle_off_by_default(u32 mwait_hint) { return false; }
#endif /* !CONFIG_ACPI_PROCESSOR_CSTATE */
static void c1e_promotion_enable(void);
/**
* ivt_idle_state_table_update - Tune the idle states table for Ivy Town.
*
@ -1570,6 +1573,26 @@ static void __init skx_idle_state_table_update(void)
}
}
/**
* spr_idle_state_table_update - Adjust Sapphire Rapids idle states table.
*/
static void __init spr_idle_state_table_update(void)
{
/* Check if user prefers C1E over C1. */
if (preferred_states_mask & BIT(2)) {
if (preferred_states_mask & BIT(1))
/* Both can't be enabled, stick to the defaults. */
return;
spr_cstates[0].flags |= CPUIDLE_FLAG_UNUSABLE;
spr_cstates[1].flags &= ~CPUIDLE_FLAG_UNUSABLE;
/* Enable C1E using the "C1E promotion" bit. */
c1e_promotion_enable();
disable_promotion_to_c1e = false;
}
}
static bool __init intel_idle_verify_cstate(unsigned int mwait_hint)
{
unsigned int mwait_cstate = MWAIT_HINT2CSTATE(mwait_hint) + 1;
@ -1604,6 +1627,9 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
case INTEL_FAM6_SKYLAKE_X:
skx_idle_state_table_update();
break;
case INTEL_FAM6_SAPPHIRERAPIDS_X:
spr_idle_state_table_update();
break;
}
for (cstate = 0; cstate < CPUIDLE_STATE_MAX; ++cstate) {
@ -1676,6 +1702,15 @@ static void auto_demotion_disable(void)
wrmsrl(MSR_PKG_CST_CONFIG_CONTROL, msr_bits);
}
static void c1e_promotion_enable(void)
{
unsigned long long msr_bits;
rdmsrl(MSR_IA32_POWER_CTL, msr_bits);
msr_bits |= 0x2;
wrmsrl(MSR_IA32_POWER_CTL, msr_bits);
}
static void c1e_promotion_disable(void)
{
unsigned long long msr_bits;
@ -1845,3 +1880,14 @@ module_param(max_cstate, int, 0444);
*/
module_param_named(states_off, disabled_states_mask, uint, 0444);
MODULE_PARM_DESC(states_off, "Mask of disabled idle states");
/*
* Some platforms come with mutually exclusive C-states, so that if one is
* enabled, the other C-states must not be used. Example: C1 and C1E on
* Sapphire Rapids platform. This parameter allows for selecting the
* preferred C-states among the groups of mutually exclusive C-states - the
* selected C-states will be registered, the other C-states from the mutually
* exclusive group won't be registered. If the platform has no mutually
* exclusive C-states, this parameter has no effect.
*/
module_param_named(preferred_cstates, preferred_states_mask, uint, 0444);
MODULE_PARM_DESC(preferred_cstates, "Mask of preferred idle states");