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Subject[PATCH v1 06/10] intel_idle: Use ACPI _CST for processor models without C-state tables
Date
From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

Modify the intel_idle driver to get the C-states information from ACPI
_CST if the processor model is not recognized by it.

The processor is still required to support MWAIT and the information
from ACPI _CST will only be used if all of the C-states listed by
_CST are of the ACPI_CSTATE_FFH type (which means that they are
expected to be entered via MWAIT).

Moreover, the driver assumes that the _CST information is the same
for all CPUs in the system, so it is sufficient to evaluate _CST for
one of them and extract the common list of C-states from there.
Also _CST is evaluated once at the system initialization time and
the driver does not respond to _CST change notifications (that can
be changed in the future).

The main functional difference between intel_idle with this change
and the ACPI processor driver is that the former sets the target
residency to be equal to the exit latency (provided by _CST) for
C1-type C-states and to 3 times the exit latency value for the other
C-state types, whereas the latter obtains the target residency by
multiplying the exit latency by the same number (2 by default) for
all C-state types. Therefore it is expected that in general using
the former instead of the latter on the same system will lead to
improved energy-efficiency.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

Changes from the RFC version:
- Subject and changelog update.
- If C-state information from _CST is used, use target residency equal to
3 times the exit latency for non C1-type C-states (was 4 times).
- Add a comment explaining the target residency generation rules.

---
drivers/idle/intel_idle.c | 190 +++++++++++++++++++++++++++++++++++++++-------
1 file changed, 162 insertions(+), 28 deletions(-)

diff --git a/drivers/idle/intel_idle.c b/drivers/idle/intel_idle.c
index 47255d3cf51f..28812d93d59a 100644
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -41,6 +41,7 @@

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt

+#include <linux/acpi.h>
#include <linux/kernel.h>
#include <linux/cpuidle.h>
#include <linux/tick.h>
@@ -1111,6 +1112,129 @@ static const struct x86_cpu_id intel_idle_ids[] __initconst = {
{}
};

+#define INTEL_CPU_FAM6_MWAIT \
+ { X86_VENDOR_INTEL, 6, X86_MODEL_ANY, X86_FEATURE_MWAIT, 0 }
+
+static const struct x86_cpu_id intel_mwait_ids[] __initconst = {
+ INTEL_CPU_FAM6_MWAIT,
+ {}
+};
+
+static bool intel_idle_max_cstate_reached(int cstate)
+{
+ if (cstate + 1 > max_cstate) {
+ pr_info("max_cstate %d reached\n", max_cstate);
+ return true;
+ }
+ return false;
+}
+
+#ifdef CONFIG_ACPI_PROCESSOR_CSTATE
+#include <acpi/processor.h>
+
+static struct acpi_processor_power acpi_state_table;
+
+/**
+ * intel_idle_cst_usable - Check if the _CST information can be used.
+ *
+ * Check if all of the C-states listed by _CST in the max_cstate range are
+ * ACPI_CSTATE_FFH, which means that they should be entered via MWAIT.
+ */
+static bool intel_idle_cst_usable(void)
+{
+ int cstate, limit;
+
+ limit = min_t(int, min_t(int, CPUIDLE_STATE_MAX, max_cstate + 1),
+ acpi_state_table.count);
+
+ for (cstate = 1; cstate < limit; cstate++) {
+ struct acpi_processor_cx *cx = &acpi_state_table.states[cstate];
+
+ if (cx->entry_method != ACPI_CSTATE_FFH)
+ return false;
+ }
+
+ return true;
+}
+
+static bool intel_idle_acpi_cst_extract(void)
+{
+ unsigned int cpu;
+
+ for_each_possible_cpu(cpu) {
+ struct acpi_processor *pr = per_cpu(processors, cpu);
+
+ if (!pr)
+ continue;
+
+ if (acpi_processor_evaluate_cst(pr->handle, cpu, &acpi_state_table))
+ continue;
+
+ acpi_state_table.count++;
+
+ if (!intel_idle_cst_usable())
+ continue;
+
+ if (!acpi_processor_claim_cst_control()) {
+ acpi_state_table.count = 0;
+ return false;
+ }
+
+ return true;
+ }
+
+ pr_debug("ACPI _CST not found or not usable\n");
+ return false;
+}
+
+static void intel_idle_init_cstates_acpi(struct cpuidle_driver *drv)
+{
+ int cstate, limit = min_t(int, CPUIDLE_STATE_MAX, acpi_state_table.count);
+
+ /*
+ * If limit > 0, intel_idle_cst_usable() has returned 'true', so all of
+ * the interesting states are ACPI_CSTATE_FFH.
+ */
+ for (cstate = 1; cstate < limit; cstate++) {
+ struct acpi_processor_cx *cx;
+ struct cpuidle_state *state;
+
+ if (intel_idle_max_cstate_reached(cstate))
+ break;
+
+ cx = &acpi_state_table.states[cstate];
+
+ state = &drv->states[drv->state_count++];
+
+ snprintf(state->name, CPUIDLE_NAME_LEN, "C%d_ACPI", cstate);
+ strlcpy(state->desc, cx->desc, CPUIDLE_DESC_LEN);
+ state->exit_latency = cx->latency;
+ /*
+ * For C1-type C-states use the same number for both the exit
+ * latency and target residency, because that is the case for
+ * C1 in the majority of the static C-states tables above.
+ * For the other types of C-states, however, set the target
+ * residency to 3 times the exit latency which should lead to
+ * a reasonable balance between energy-efficiency and
+ * performance in the majority of interesting cases.
+ */
+ state->target_residency = cx->latency;
+ if (cx->type > ACPI_STATE_C1)
+ state->target_residency *= 3;
+
+ state->flags = MWAIT2flg(cx->address);
+ if (cx->type > ACPI_STATE_C2)
+ state->flags |= CPUIDLE_FLAG_TLB_FLUSHED;
+
+ state->enter = intel_idle;
+ state->enter_s2idle = intel_idle_s2idle;
+ }
+}
+#else /* !CONFIG_ACPI_PROCESSOR_CSTATE */
+static inline bool intel_idle_acpi_cst_extract(void) { return false; }
+static inline void intel_idle_init_cstates_acpi(struct cpuidle_driver *drv) { }
+#endif /* !CONFIG_ACPI_PROCESSOR_CSTATE */
+
/*
* intel_idle_probe()
*/
@@ -1125,17 +1249,15 @@ static int __init intel_idle_probe(void)
}

id = x86_match_cpu(intel_idle_ids);
- if (!id) {
- if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
- boot_cpu_data.x86 == 6)
- pr_debug("does not run on family %d model %d\n",
- boot_cpu_data.x86, boot_cpu_data.x86_model);
- return -ENODEV;
- }
-
- if (!boot_cpu_has(X86_FEATURE_MWAIT)) {
- pr_debug("Please enable MWAIT in BIOS SETUP\n");
- return -ENODEV;
+ if (id) {
+ if (!boot_cpu_has(X86_FEATURE_MWAIT)) {
+ pr_debug("Please enable MWAIT in BIOS SETUP\n");
+ return -ENODEV;
+ }
+ } else {
+ id = x86_match_cpu(intel_mwait_ids);
+ if (!id)
+ return -ENODEV;
}

if (boot_cpu_data.cpuid_level < CPUID_MWAIT_LEAF)
@@ -1151,7 +1273,10 @@ static int __init intel_idle_probe(void)
pr_debug("MWAIT substates: 0x%x\n", mwait_substates);

icpu = (const struct idle_cpu *)id->driver_data;
- cpuidle_state_table = icpu->state_table;
+ if (icpu)
+ cpuidle_state_table = icpu->state_table;
+ else if (!intel_idle_acpi_cst_extract())
+ return -ENODEV;

pr_debug("v" INTEL_IDLE_VERSION " model 0x%X\n",
boot_cpu_data.x86_model);
@@ -1333,31 +1458,19 @@ static void intel_idle_state_table_update(void)
}
}

-/*
- * intel_idle_cpuidle_driver_init()
- * allocate, initialize cpuidle_states
- */
-static void __init intel_idle_cpuidle_driver_init(void)
+static void intel_idle_init_cstates_icpu(struct cpuidle_driver *drv)
{
int cstate;
- struct cpuidle_driver *drv = &intel_idle_driver;
-
- intel_idle_state_table_update();
-
- cpuidle_poll_state_init(drv);
- drv->state_count = 1;

for (cstate = 0; cstate < CPUIDLE_STATE_MAX; ++cstate) {
unsigned int mwait_hint;

- if (!cpuidle_state_table[cstate].enter &&
- !cpuidle_state_table[cstate].enter_s2idle)
+ if (intel_idle_max_cstate_reached(cstate))
break;

- if (cstate + 1 > max_cstate) {
- pr_info("max_cstate %d reached\n", max_cstate);
+ if (!cpuidle_state_table[cstate].enter &&
+ !cpuidle_state_table[cstate].enter_s2idle)
break;
- }

/* If marked as unusable, skip this state. */
if (cpuidle_state_table[cstate].flags & CPUIDLE_FLAG_UNUSABLE) {
@@ -1380,6 +1493,24 @@ static void __init intel_idle_cpuidle_driver_init(void)
}
}

+/*
+ * intel_idle_cpuidle_driver_init()
+ * allocate, initialize cpuidle_states
+ */
+static void __init intel_idle_cpuidle_driver_init(void)
+{
+ struct cpuidle_driver *drv = &intel_idle_driver;
+
+ intel_idle_state_table_update();
+
+ cpuidle_poll_state_init(drv);
+ drv->state_count = 1;
+
+ if (icpu)
+ intel_idle_init_cstates_icpu(drv);
+ else
+ intel_idle_init_cstates_acpi(drv);
+}

/*
* intel_idle_cpu_init()
@@ -1398,6 +1529,9 @@ static int intel_idle_cpu_init(unsigned int cpu)
return -EIO;
}

+ if (!icpu)
+ return 0;
+
if (icpu->auto_demotion_disable_flags)
auto_demotion_disable();

--
2.16.4




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