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Subject[PATCH v5 2/2] 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.

Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Tested-by : Zhang Rui <rui.zhang@intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: linux-pm@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Len Brown <lenb@kernel.org>
---
Changes from v2:
* Remove an unnecessary backslash (Rafael Wysocki).

Changes from v1:
* Simplify the code with a new flag (Rui).
* Rebase on Artem's patches for SPR intel_idle.
* Massage the changelog.
---
drivers/idle/intel_idle.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index b9bb94bd0f67..5f36c4b28f9d 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)
@@ -139,6 +145,9 @@ static __cpuidle int intel_idle(struct cpuidle_device *dev,
if (state->flags & CPUIDLE_FLAG_IRQ_ENABLE)
local_irq_enable();

+ if (state->flags & CPUIDLE_FLAG_INIT_XSTATE)
+ fpu_idle_fpregs();
+
mwait_idle_with_hints(eax, ecx);

return index;
@@ -159,8 +168,12 @@ static __cpuidle int intel_idle(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);

@@ -895,7 +908,8 @@ 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,
--
2.17.1
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