ACPI deep C-state entry had a long standing bug/missing feature, wherein we were sending
resched IPIs when an idle CPU is in mwait based deep C-state. Only mwait based C1 was using
the write to the monitored address to wake up mwait'ing CPU.
This patch changes the code to retain TS_POLLING bit if we are entering an mwait based
deep C-state.
The patch has been verified to reduce the number of resched IPIs in general and also
improves the performance/power on workloads with low system utilization (i.e., when mwait based
deep C-states are being used).
Reported-by: Lin Ming <ming.m.lin@xxxxxxxxx>
Tested-by: Alex Shi <alex.shi@xxxxxxxxx>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@xxxxxxxxx>
---
drivers/acpi/processor_idle.c | 28 ++++++++++++++++------------
1 files changed, 16 insertions(+), 12 deletions(-)
diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index 7c0441f..8abe91a 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -872,12 +872,14 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
return(acpi_idle_enter_c1(dev, state));
local_irq_disable();
- current_thread_info()->status &= ~TS_POLLING;
- /*
- * TS_POLLING-cleared state must be visible before we test
- * NEED_RESCHED:
- */
- smp_mb();
+ if (cx->entry_method != ACPI_CSTATE_FFH) {
+ current_thread_info()->status &= ~TS_POLLING;
+ /*
+ * TS_POLLING-cleared state must be visible before we test
+ * NEED_RESCHED:
+ */
+ smp_mb();
+ }
if (unlikely(need_resched())) {
current_thread_info()->status |= TS_POLLING;
@@ -957,12 +959,14 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
}
local_irq_disable();
- current_thread_info()->status &= ~TS_POLLING;
- /*
- * TS_POLLING-cleared state must be visible before we test
- * NEED_RESCHED:
- */
- smp_mb();
+ if (cx->entry_method != ACPI_CSTATE_FFH) {
+ current_thread_info()->status &= ~TS_POLLING;
+ /*
+ * TS_POLLING-cleared state must be visible before we test
+ * NEED_RESCHED:
+ */
+ smp_mb();
+ }
if (unlikely(need_resched())) {
current_thread_info()->status |= TS_POLLING;
--
1.6.0.6
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