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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). Fixes "netperf ~50% regression with 2.6.33-rc1, bisect to 1b9508f" http://marc.info/?l=linux-kernel&m=126441481427331&w=4 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> Signed-off-by: Len Brown <len.brown@intel.com>
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1 changed files with 16 additions and 12 deletions
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@ -880,12 +880,14 @@ static int acpi_idle_enter_simple(struct cpuidle_device *dev,
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return(acpi_idle_enter_c1(dev, state));
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local_irq_disable();
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current_thread_info()->status &= ~TS_POLLING;
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/*
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* TS_POLLING-cleared state must be visible before we test
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* NEED_RESCHED:
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*/
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smp_mb();
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if (cx->entry_method != ACPI_CSTATE_FFH) {
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current_thread_info()->status &= ~TS_POLLING;
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/*
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* TS_POLLING-cleared state must be visible before we test
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* NEED_RESCHED:
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*/
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smp_mb();
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}
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if (unlikely(need_resched())) {
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current_thread_info()->status |= TS_POLLING;
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@ -965,12 +967,14 @@ static int acpi_idle_enter_bm(struct cpuidle_device *dev,
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}
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local_irq_disable();
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current_thread_info()->status &= ~TS_POLLING;
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/*
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* TS_POLLING-cleared state must be visible before we test
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* NEED_RESCHED:
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*/
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smp_mb();
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if (cx->entry_method != ACPI_CSTATE_FFH) {
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current_thread_info()->status &= ~TS_POLLING;
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/*
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* TS_POLLING-cleared state must be visible before we test
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* NEED_RESCHED:
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*/
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smp_mb();
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}
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if (unlikely(need_resched())) {
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current_thread_info()->status |= TS_POLLING;
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