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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen staging] x86/mwait-idle: Add cmdline option to adjust C-states table
commit 78c159bdf631c1270ca4feb813e7a82a5af3cc67
Author: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
AuthorDate: Mon May 18 08:57:36 2026 +0200
Commit: Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon May 18 08:57:36 2026 +0200
x86/mwait-idle: Add cmdline option to adjust C-states table
Add a new module parameter that allows adjusting the C-states table used by
the driver.
Currently, the C-states table is hardcoded in the driver based on the CPU
model. The goal is to have good enough defaults for most users.
However, C-state characteristics, such as exit latency and residency, can
vary between different variants of the same CPU model and BIOS settings.
Moreover, different platform usage models and user preferences may benefit
from different C-state target_residency values.
Provide a way for users to adjust the C-states table via a module parameter
"table". The general format is:
"state1:latency1:target_residency1,state2:latency2:target_residency2,..."
In other words, represent each C-state by its name, exit latency (in
microseconds), and target residency (in microseconds), separated by colons.
Separate multiple C-states by commas.
For example, suppose a CPU has 3 C-states with the following
characteristics:
C1: exit_latency=1, target_residency=2
C1E: exit_latency=10, target_residency=10
C6: exit_latency=100, target_residency=500
Users can specify a custom C-states table as follows:
1. intel_idle.table="C1:2:2,C1E:5:20,C6:150:600"
Result: C1: exit_latency=2, target_residency=2
C1E: exit_latency=5, target_residency=20
C6: exit_latency=150, target_residency=600
2. intel_idle.table="C6::400"
Result: C1: exit_latency=1, target_residency=2 (unchanged)
C1E: exit_latency=10, target_residency=10 (unchanged)
C6: exit_latency=100, target_residency=400
(only target_residency changed)
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
Link: https://patch.msgid.link/20251216080402.156988-3-dedekind1@xxxxxxxxx
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Origin: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
111f77a23348
Add __init to get_cmdline_field(). Put cmdline_table_str[] in .init.data.
Other adjustments to fit our env.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
docs/misc/xen-command-line.pandoc | 17 ++++
xen/arch/x86/cpu/mwait-idle.c | 165 ++++++++++++++++++++++++++++++++++++++
2 files changed, 182 insertions(+)
diff --git a/docs/misc/xen-command-line.pandoc
b/docs/misc/xen-command-line.pandoc
index 72da2f2584..52d4ca0f2f 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1920,6 +1920,23 @@ Print boot time MTRR state.
Use the MWAIT idle driver (with model specific C-state knowledge) instead
of the ACPI based one.
+### mwait-idle.table (x86)
+> `= <string>`
+
+ Define the C-states table from a user input string. Expected format is
+ 'name:latency:residency', where:
+ - name: The C-state name.
+ - latency: The C-state exit latency in us.
+ - residency: The C-state target residency in us.
+
+ Multiple C-states can be defined by separating them with commas:
+ 'name1:latency1:residency1,name2:latency2:residency2'
+
+ Example: mwait-idle.table=C1:1:1,C1E:5:10,C6:100:600
+
+ To leave latency or residency unchanged, use an empty field, for example:
+ 'C1:1:1,C1E::10' - leaves C1E latency unchanged.
+
### nmi (x86)
> `= ignore | dom0 | fatal`
diff --git a/xen/arch/x86/cpu/mwait-idle.c b/xen/arch/x86/cpu/mwait-idle.c
index c8d15faf40..4d5223d9d5 100644
--- a/xen/arch/x86/cpu/mwait-idle.c
+++ b/xen/arch/x86/cpu/mwait-idle.c
@@ -70,6 +70,11 @@
static __initdata bool opt_mwait_idle = true;
boolean_param("mwait-idle", opt_mwait_idle);
+/* The maximum allowed length for the 'table' module parameter */
+#define MAX_CMDLINE_TABLE_LEN 256
+static char cmdline_table_str[MAX_CMDLINE_TABLE_LEN] __initdata;
+string_param("mwait-idle.table", cmdline_table_str);
+
static unsigned int mwait_substates;
#define LAPIC_TIMER_ALWAYS_RELIABLE 0xFFFFFFFF
@@ -122,6 +127,9 @@ struct cpuidle_state {
*/
#define CPUIDLE_FLAG_IBRS 0x20000
+/* C-states data from the 'mwait-idle.table' cmdline parameter */
+static struct cpuidle_state cmdline_states[ACPI_PROCESSOR_MAX_POWER]
__initdata;
+
/*
* MWAIT takes an 8-bit "hint" in EAX "suggesting"
* the C-state (top nibble) and sub-state (bottom nibble)
@@ -1547,6 +1555,161 @@ static void __init mwait_idle_state_table_update(void)
}
}
+ /**
+ * get_cmdline_field - Get the current field from a cmdline string.
+ * @args: The cmdline string to get the current field from.
+ * @field: Pointer to the current field upon return.
+ * @sep: The fields separator character.
+ *
+ * Examples:
+ * Input: args="C1:1:1,C1E:2:10", sep=':'
+ * Output: field="C1", return "1:1,C1E:2:10"
+ * Input: args="C1:1:1,C1E:2:10", sep=','
+ * Output: field="C1:1:1", return "C1E:2:10"
+ * Ipnut: args="::", sep=':'
+ * Output: field="", return ":"
+ *
+ * Return: The continuation of the cmdline string after the field or NULL.
+ */
+static char *__init get_cmdline_field(char *args, char **field, char sep)
+{
+ unsigned int i;
+
+ for (i = 0; args[i] && !isspace(args[i]); i++) {
+ if (args[i] == sep)
+ break;
+ }
+
+ *field = args;
+
+ if (args[i] != sep)
+ return NULL;
+
+ args[i] = '\0';
+ return args + i + 1;
+}
+
+/**
+ * cmdline_table_adjust - Adjust the C-states table with data from cmdline.
+ *
+ * Adjust the C-states table with data from the 'mwait-idle.table' parameter
+ * (if specified).
+ */
+static void __init cmdline_table_adjust(void)
+{
+ char *args = cmdline_table_str;
+ struct cpuidle_state *state;
+ unsigned int i, state_count;
+
+ if (args[0] == '\0')
+ /* The 'mwait-idle.table' module parameter was not specified */
+ return;
+
+ /* Create a copy of the C-states table */
+ for (i = 0;
+ i < ARRAY_SIZE(cmdline_states) && icpu.state_table[i].name[0];
+ i++)
+ cmdline_states[i] = icpu.state_table[i];
+
+ state_count = i;
+
+ /*
+ * Adjust the C-states table copy with data from the 'mwait-idle.table'
+ * module parameter.
+ */
+ while (args) {
+ char *fields, *name, *val;
+
+ /*
+ * Get the next C-state definition, which is expected to be
+ * '<name>:<latency_us>:<target_residency_us>'. Treat "empty"
+ * fields as unchanged. For example,
+ * '<name>::<target_residency_us>' leaves the latency unchanged.
+ */
+ args = get_cmdline_field(args, &fields, ',');
+
+ /* name */
+ fields = get_cmdline_field(fields, &name, ':');
+ if (!fields)
+ goto error;
+
+ /* Find the C-state by its name */
+ state = NULL;
+ for (i = 0; i < state_count; i++) {
+ if (!strcmp(name, cmdline_states[i].name)) {
+ state = &cmdline_states[i];
+ break;
+ }
+ }
+
+ if (!state) {
+ printk(XENLOG_ERR PREFIX "C-state '%s' was not found\n",
+ name);
+ continue;
+ }
+
+ /* Latency */
+ fields = get_cmdline_field(fields, &val, ':');
+ if (!fields)
+ goto error;
+
+ if (*val) {
+ const char *end;
+ unsigned long n = simple_strtoul(val, &end, 0);
+
+ state->exit_latency = n;
+ if (*end || state->exit_latency != n)
+ goto error;
+ }
+
+ /* Target residency */
+ fields = get_cmdline_field(fields, &val, ':');
+
+ if (*val) {
+ const char *end;
+ unsigned long n = simple_strtoul(val, &end, 0);
+
+ state->target_residency = n;
+ if (*end || state->target_residency != n)
+ goto error;
+ }
+
+ /*
+ * Allow for 3 more fields, but ignore them. Helps to make
+ * possible future extensions of the cmdline format backward
+ * compatible.
+ */
+ for (i = 0; fields && i < 3; i++) {
+ fields = get_cmdline_field(fields, &val, ':');
+ if (!fields)
+ break;
+ }
+
+ if (fields) {
+ printk(XENLOG_ERR PREFIX
+ "Too many fields for C-state '%s'\n",
+ state->name);
+ goto error;
+ }
+
+ printk(XENLOG_INFO PREFIX
+ "C-state from cmdline: name=%s, latency=%u,
residency=%u\n",
+ state->name, state->exit_latency,
state->target_residency);
+ }
+
+ /* Copy the adjusted C-states table back */
+ for (i = 0; i < state_count; i++)
+ icpu.state_table[i] = cmdline_states[i];
+
+ printk(XENLOG_INFO PREFIX
+ "Adjusted C-states with data from 'mwait-idle.table'\n");
+ return;
+
+ error:
+ printk(XENLOG_WARNING PREFIX
+ "Failed to adjust C-states with data from 'mwait-idle.table'\n");
+}
+
static int __init mwait_idle_probe(void)
{
unsigned int eax, ebx, ecx;
@@ -1596,6 +1759,8 @@ static int __init mwait_idle_probe(void)
mwait_idle_state_table_update();
+ cmdline_table_adjust();
+
return 0;
}
--
generated by git-patchbot for /home/xen/git/xen.git#staging
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