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Subject[PATCH][Rebased] intel_idle: Add a new flag to initialize the AMX state
Date
The non-initialized AMX state can be the cause of C-state demotion from C6
to C1E. This low-power idle state may improve power savings and thus result
in a higher available turbo frequency budget.

This behavior is implementation-specific. Initialize the state for the C6
entrance of Sapphire Rapids as needed.

Tested-by: Zhang Rui <rui.zhang@intel.com>
Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Link: https://lkml.kernel.org/r/20220608164748.11864-3-chang.seok.bae@intel.com
[changb: Rebase to the upstream with peterz's help]
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
---
The patch merged in the tip's x86/fpu branch [1] has conflict with the
upstream -- commit 32d4fd5751ea ("cpuidle,intel_idle: Fix
CPUIDLE_FLAG_IRQ_ENABLE") as of v5.19-rc2.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=x86/fpu
---
drivers/idle/intel_idle.c | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 424ef470223d..8a19ba1c2c1b 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -54,6 +54,7 @@
#include <asm/intel-family.h>
#include <asm/mwait.h>
#include <asm/msr.h>
+#include <asm/fpu/api.h>

#define INTEL_IDLE_VERSION "0.5.1"

@@ -105,6 +106,11 @@ static unsigned int mwait_substates __initdata;
*/
#define CPUIDLE_FLAG_ALWAYS_ENABLE BIT(15)

+/*
+ * Initialize large xstate for the C6-state entrance.
+ */
+#define CPUIDLE_FLAG_INIT_XSTATE BIT(16)
+
/*
* MWAIT takes an 8-bit "hint" in EAX "suggesting"
* the C-state (top nibble) and sub-state (bottom nibble)
@@ -159,6 +165,13 @@ static __cpuidle int intel_idle_irq(struct cpuidle_device *dev,
return ret;
}

+static __cpuidle int intel_idle_xstate(struct cpuidle_device *dev,
+ struct cpuidle_driver *drv, int index)
+{
+ fpu_idle_fpregs();
+ return __intel_idle(dev, drv, index);
+}
+
/**
* intel_idle_s2idle - Ask the processor to enter the given idle state.
* @dev: cpuidle device of the target CPU.
@@ -174,8 +187,12 @@ static __cpuidle int intel_idle_irq(struct cpuidle_device *dev,
static __cpuidle int intel_idle_s2idle(struct cpuidle_device *dev,
struct cpuidle_driver *drv, int index)
{
- unsigned long eax = flg2MWAIT(drv->states[index].flags);
unsigned long ecx = 1; /* break on interrupt flag */
+ struct cpuidle_state *state = &drv->states[index];
+ unsigned long eax = flg2MWAIT(state->flags);
+
+ if (state->flags & CPUIDLE_FLAG_INIT_XSTATE)
+ fpu_idle_fpregs();

mwait_idle_with_hints(eax, ecx);

@@ -910,7 +927,8 @@ static struct cpuidle_state spr_cstates[] __initdata = {
{
.name = "C6",
.desc = "MWAIT 0x20",
- .flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED,
+ .flags = MWAIT2flg(0x20) | CPUIDLE_FLAG_TLB_FLUSHED |
+ CPUIDLE_FLAG_INIT_XSTATE,
.exit_latency = 290,
.target_residency = 800,
.enter = &intel_idle,
@@ -1819,6 +1837,9 @@ static void __init intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
if (cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_IRQ_ENABLE)
drv->states[drv->state_count].enter = intel_idle_irq;

+ if (cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_INIT_XSTATE)
+ drv->states[drv->state_count].enter = intel_idle_xstate;
+
if ((disabled_states_mask & BIT(drv->state_count)) ||
((icpu->use_acpi || force_use_acpi) &&
intel_idle_off_by_default(mwait_hint) &&
--
2.17.1
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