The branch main has been updated by jhibbits:
URL:
https://cgit.FreeBSD.org/src/commit/?id=58f77309c4e0d3373705582e9ca7649fe74dd267
commit 58f77309c4e0d3373705582e9ca7649fe74dd267
Author: Timothy Pearson <tpear...@raptorengineering.com>
AuthorDate: 2025-01-20 20:03:55 +0000
Commit: Justin Hibbits <jhibb...@freebsd.org>
CommitDate: 2025-01-21 23:14:40 +0000
Add machdep.cpu_idle_max_stop_state tunable
Multiple idle and deep sleep states are supported on Power7+ platforms, with
each state having a characteristic latency and effect on system real-time
performance.
Add a tunable to allow a maximum sleep state (maximum theoretical
sleep-related
latency) to be set, in order to better support specific latency-sensitive
applications / real time workloads.
Signed-off-by: Timothy Pearson <tpear...@raptorengineering.com>
---
sys/powerpc/powerpc/cpu.c | 40 +++++++++++++++++++++++++++++++++++++++-
1 file changed, 39 insertions(+), 1 deletion(-)
diff --git a/sys/powerpc/powerpc/cpu.c b/sys/powerpc/powerpc/cpu.c
index f73ed25c8924..4b8da50cf642 100644
--- a/sys/powerpc/powerpc/cpu.c
+++ b/sys/powerpc/powerpc/cpu.c
@@ -95,6 +95,9 @@ static void cpu_idle_booke(sbintime_t);
static void cpu_idle_e500mc(sbintime_t sbt);
#endif
#if defined(__powerpc64__) && defined(AIM)
+static int cpu_idle_max_stop_state = 2;
+SYSCTL_INT(_machdep, OID_AUTO, cpu_idle_max_stop_state,
+ CTLFLAG_RW, &cpu_idle_max_stop_state, 0, "");
static void cpu_idle_powerx(sbintime_t);
static void cpu_idle_power9(sbintime_t);
#endif
@@ -815,6 +818,22 @@ cpu_idle_booke(sbintime_t sbt)
static void
cpu_idle_powerx(sbintime_t sbt)
{
+ int max_stop_state = cpu_idle_max_stop_state;
+
+ /* Limit maximum stop state to valid values */
+ if (max_stop_state < 0) {
+ /* Don't nap at all, busy wait instead */
+ cpu_idle_max_stop_state = -1;
+ return;
+ }
+ if (max_stop_state > 1) {
+ /* POWER8 and below only support the one stop state,
+ * i.e. 'nap'
+ */
+ max_stop_state = 1;
+ cpu_idle_max_stop_state = max_stop_state;
+ }
+
/* Sleeping when running on one cpu gives no advantages - avoid it */
if (smp_started == 0)
return;
@@ -837,9 +856,28 @@ static void
cpu_idle_power9(sbintime_t sbt)
{
register_t msr;
+ int max_stop_state = cpu_idle_max_stop_state;
- msr = mfmsr();
+ /* Limit maximum stop state to valid values */
+ if (max_stop_state < 0) {
+ /* Don't stop at all, busy wait instead */
+ cpu_idle_max_stop_state = -1;
+ return;
+ }
+
+ /* Set maximum transition level to 3, for deepest lossless sleep.
+ * On POWER9 this is automatically downgraded to the next supported
+ * stop state (stop2), but other CPUs may support stop3.
+ */
+ if (max_stop_state > 3) {
+ /* Stop states greater than 3 require register state save and
+ * restore functionality that is not yet implemented
+ */
+ max_stop_state = 3;
+ cpu_idle_max_stop_state = max_stop_state;
+ }
+ msr = mfmsr();
/* Suspend external interrupts until stop instruction completes. */
mtmsr(msr & ~PSL_EE);
/* Set the stop state to lowest latency, wake up to next instruction */
