2010-02-10 18:35:40

by Pallipadi, Venkatesh

Subject: [PATCH] acpi: Be in TS_POLLING state during mwait based C-state entry

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 <[email protected]>
Tested-by: Alex Shi <[email protected]>

Signed-off-by: Venkatesh Pallipadi <[email protected]>

---
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

2010-02-22 18:10:54

by Len Brown

Subject: Re: [PATCH] acpi: Be in TS_POLLING state during mwait based C-state entry

applied

thanks,
Len Brown, Intel Open Source Technology Center