1. 27 9月, 2009 1 次提交
  2. 01 8月, 2009 1 次提交
    • S
      ACPI: create Processor Aggregator Device driver · 8e0af514
      Shaohua Li 提交于
      ACPI 4.0 created the logical "processor aggregator device" as
      a mechinism for platforms to ask the OS to force otherwise busy
      processors to enter (power saving) idle.
      
      The intent is to lower power consumption to ride-out
      transient electrical and thermal emergencies,
      rather than powering off the server.
      
      On platforms that can save more power/performance via P-states,
      the platform will first exhaust P-states before forcing idle.
      However, the relative benefit of P-states vs. idle states
      is platform dependent, and thus this driver need not know
      or care about it.
      
      This driver does not use the kernel's CPU hot-plug mechanism
      because after the transient emergency is over, the system must
      be returned to its normal state, and hotplug would permanently
      break both cpusets and binding.
      
      So to force idle, the driver creates a power saving thread.
      The scheduler will migrate the thread to the preferred CPU.
      The thread has max priority and has SCHED_RR policy,
      so it can occupy one CPU.  To save power, the thread will
      invoke the deep C-state entry instructions.
      
      To avoid starvation, the thread will sleep 5% of the time
      time for every second (current RT scheduler has threshold
      to avoid starvation, but if other CPUs are idle,
      the CPU can borrow CPU timer from other,
      which makes the mechanism not work here)
      
      Vaidyanathan Srinivasan has proposed scheduler enhancements
      to allow injecting idle time into the system.  This driver doesn't
      depend on those enhancements, but could cut over to them
      when they are available.
      
      Peter Z. does not favor upstreaming this driver until
      the those scheduler enhancements are in place.  However,
      we favor upstreaming this driver now because it is useful
      now, and can be enhanced over time.
      Signed-off-by: NShaohua Li <shaohua.li@intel.com>
      NACKed-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
      Cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
      Signed-off-by: NLen Brown <len.brown@intel.com>
      8e0af514
  3. 23 7月, 2009 33 次提交
  4. 22 7月, 2009 5 次提交