Messages in this thread Patch in this message | | | Date | Wed, 10 Feb 2010 10:35:31 -0800 | From | "Pallipadi, Venkatesh" <> | Subject | [PATCH] acpi: Be in TS_POLLING state during mwait based C-state entry |
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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@intel.com> Tested-by: Alex Shi <alex.shi@intel.com>
Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
--- 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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