linux-toradex.git/drivers/acpi/processor_idle.c, branch v2.6.20.19

Merge branch 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6

2006-12-23T02:46:56+00:00

* 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6: (68 commits)
  ACPI: replace kmalloc+memset with kzalloc
  ACPI: Add support for acpi_load_table/acpi_unload_table_id
  fbdev: update after backlight argument change
  ACPI: video: Add dev argument for backlight_device_register
  ACPI: Implement acpi_video_get_next_level()
  ACPI: Kconfig - depend on PM rather than selecting it
  ACPI: fix NULL check in drivers/acpi/osl.c
  ACPI: make drivers/acpi/ec.c:ec_ecdt static
  ACPI: prevent processor module from loading on failures
  ACPI: fix single linked list manipulation
  ACPI: ibm_acpi: allow clean removal
  ACPI: fix git automerge failure
  ACPI: ibm_acpi: respond to workqueue update
  ACPI: dock: add uevent to indicate change in device status
  ACPI: ec: Lindent once again
  ACPI: ec: Change #define to enums there possible.
  ACPI: ec: Style changes.
  ACPI: ec: Acquire Global Lock under EC mutex.
  ACPI: ec: Drop udelay() from poll mode. Loop by reading status field instead.
  ACPI: ec: Rename gpe_bit to gpe
  ...

[PATCH] sched: fix bad missed wakeups in the i386, x86_64, ia64, ACPI and APM idle code

2006-12-22T16:55:51+00:00

Fernando Lopez-Lezcano reported frequent scheduling latencies and audio
xruns starting at the 2.6.18-rt kernel, and those problems persisted all
until current -rt kernels. The latencies were serious and unjustified by
system load, often in the milliseconds range.

After a patient and heroic multi-month effort of Fernando, where he
tested dozens of kernels, tried various configs, boot options,
test-patches of mine and provided latency traces of those incidents, the
following 'smoking gun' trace was captured by him:

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
  IRQ_19-1479  1D..1    0us : __trace_start_sched_wakeup (try_to_wake_up)
  IRQ_19-1479  1D..1    0us : __trace_start_sched_wakeup <<...>-5856> (37 0)
  IRQ_19-1479  1D..1    0us : __trace_start_sched_wakeup (c01262ba 0 0)
  IRQ_19-1479  1D..1    0us : resched_task (try_to_wake_up)
  IRQ_19-1479  1D..1    0us : __spin_unlock_irqrestore (try_to_wake_up)
  ...
  -0     1...1   11us!: default_idle (cpu_idle)
  ...
  -0     0Dn.1  602us : smp_apic_timer_interrupt (c0103baf 1 0)
  ...
   <...>-5856  0D..2  618us : __switch_to (__schedule)
   <...>-5856  0D..2  618us : __schedule <-0> (20 162)
   <...>-5856  0D..2  619us : __spin_unlock_irq (__schedule)
   <...>-5856  0...1  619us : trace_stop_sched_switched (__schedule)
   <...>-5856  0D..1  619us : trace_stop_sched_switched <<...>-5856> (37 0)

what is visible in this trace is that CPU#1 ran try_to_wake_up() for
PID:5856, it placed PID:5856 on CPU#0's runqueue and ran resched_task()
for CPU#0. But it decided to not send an IPI that no CPU - due to
TS_POLLING. But CPU#0 never woke up after its NEED_RESCHED bit was set,
and only rescheduled to PID:5856 upon the next lapic timer IRQ. The
result was a 600+ usecs latency and a missed wakeup!

the bug turned out to be an idle-wakeup bug introduced into the mainline
kernel this summer via an optimization in the x86_64 tree:

    commit 495ab9c045e1b0e5c82951b762257fe1c9d81564
    Author: Andi Kleen 
    Date:   Mon Jun 26 13:59:11 2006 +0200

    [PATCH] i386/x86-64/ia64: Move polling flag into thread_info_status

    During some profiling I noticed that default_idle causes a lot of
    memory traffic. I think that is caused by the atomic operations
    to clear/set the polling flag in thread_info. There is actually
    no reason to make this atomic - only the idle thread does it
    to itself, other CPUs only read it. So I moved it into ti->status.

the problem is this type of change:

        if (!hlt_counter && boot_cpu_data.hlt_works_ok) {
-               clear_thread_flag(TIF_POLLING_NRFLAG);
+               current_thread_info()->status &= ~TS_POLLING;
                smp_mb__after_clear_bit();
                while (!need_resched()) {
                        local_irq_disable();

this changes clear_thread_flag() to an explicit clearing of TS_POLLING.
clear_thread_flag() is defined as:

        clear_bit(flag, &ti->flags);

and clear_bit() is a LOCK-ed atomic instruction on all x86 platforms:

  static inline void clear_bit(int nr, volatile unsigned long * addr)
  {
          __asm__ __volatile__( LOCK_PREFIX
                  "btrl %1,%0"

hence smp_mb__after_clear_bit() is defined as a simple compile barrier:

  #define smp_mb__after_clear_bit()       barrier()

but the explicit TS_POLLING clearing introduced by the patch:

+               current_thread_info()->status &= ~TS_POLLING;

is not an atomic op! So the clearing of the TS_POLLING bit is freely
reorderable with the reading of the NEED_RESCHED bit - and both now
reside in different memory addresses.

CPU idle wakeup very much depends on ordered memory ops, the clearing of
the TS_POLLING flag must always be done before we test need_resched()
and hit the idle instruction(s). [Symmetrically, the wakeup code needs
to set NEED_RESCHED before it tests the TS_POLLING flag, so memory
ordering is paramount.]

Fernando's dual-core Athlon64 system has a sufficiently advanced memory
ordering model so that it triggered this scenario very often.

( And it also turned out that the reason why these latencies never
  triggered on my testsystems is that i routinely use idle=poll, which
  was the only idle variant not affected by this bug. )

The fix is to change the smp_mb__after_clear_bit() to an smp_mb(), to
act as an absolute barrier between the TS_POLLING write and the
NEED_RESCHED read. This affects almost all idling methods (default,
ACPI, APM), on all 3 x86 architectures: i386, x86_64, ia64.

Signed-off-by: Ingo Molnar 
Tested-by: Fernando Lopez-Lezcano 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Pull style into test branch

2006-12-16T06:04:27+00:00

Conflicts:

	drivers/acpi/button.c
	drivers/acpi/ec.c
	drivers/acpi/osl.c
	drivers/acpi/sbs.c

[PATCH] fix "ACPI: Processor native C-states using MWAIT"

2006-10-20T17:26:37+00:00

This patch breaks C-state discovery on my IBM IntelliStation Z30 because
the return value of acpi_processor_get_power_info_fadt is not assigned to
"result" in the case that acpi_processor_get_power_info_cst returns
-ENODEV.  Thus, if ACPI provides C-state data via the FADT and not _CST (as
is the case on this machine), we incorrectly exit the function with -ENODEV
after reading the FADT.  The attached patch sets the value of result so
that we don't exit early.

Signed-off-by: Darrick J. Wong 
Acked-by: "Pallipadi, Venkatesh" 
Acked-by: "Brown, Len" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

[PATCH] acpi_processor_latency_notifier(): UP warning fix

2006-10-17T15:18:44+00:00

drivers/acpi/processor_idle.c:1112: warning: 'smp_callback' defined but not used

Cc: Len Brown 
Cc: Arjan van de Ven 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Pull trivial into test branch

2006-10-14T06:28:07+00:00

ACPI: fix section for CPU init functions

2006-10-14T05:58:38+00:00

The ACPI processor init functions should be marked as __cpuinit as they use
structures marked with __cpuinitdata.

Signed-off-by: Pierre Ossman 
Signed-off-by: Andrew Morton 
Signed-off-by: Len Brown

ACPI: Remove unnecessary from/to-void* and to-void casts in drivers/acpi

2006-10-14T05:51:07+00:00

Signed-off-by: Jan Engelhardt 
Signed-off-by: Len Brown

ACPI: Processor native C-states using MWAIT

2006-10-14T04:35:39+00:00

Intel processors starting with the Core Duo support
support processor native C-state using the MWAIT instruction.
Refer: Intel Architecture Software Developer's Manual
http://www.intel.com/design/Pentium4/manuals/253668.htm

Platform firmware exports the support for Native C-state to OS using
ACPI _PDC and _CST methods.
Refer: Intel Processor Vendor-Specific ACPI: Interface Specification
http://www.intel.com/technology/iapc/acpi/downloads/302223.htm

With Processor Native C-state, we use 'MWAIT' instruction on the processor
to enter different C-states (C1, C2, C3).  We won't use the special IO
ports to enter C-state and no SMM mode etc required to enter C-state.
Overall this will mean better C-state support.

One major advantage of using MWAIT for all C-states is, with this and
"treat interrupt as break event" feature of MWAIT, we can now get accurate
timing for the time spent in C1, C2, ..  states.

Signed-off-by: Venkatesh Pallipadi 
Signed-off-by: Andrew Morton 
Signed-off-by: Len Brown

[PATCH] maximum latency tracking infrastructure

2006-10-01T07:39:19+00:00

Add infrastructure to track "maximum allowable latency" for power saving
policies.

The reason for adding this infrastructure is that power management in the
idle loop needs to make a tradeoff between latency and power savings
(deeper power save modes have a longer latency to running code again).  The
code that today makes this tradeoff just does a rather simple algorithm;
however this is not good enough: There are devices and use cases where a
lower latency is required than that the higher power saving states provide.
 An example would be audio playback, but another example is the ipw2100
wireless driver that right now has a very direct and ugly acpi hook to
disable some higher power states randomly when it gets certain types of
error.

The proposed solution is to have an interface where drivers can

* announce the maximum latency (in microseconds) that they can deal with
* modify this latency
* give up their constraint

and a function where the code that decides on power saving strategy can
query the current global desired maximum.

This patch has a user of each side: on the consumer side, ACPI is patched
to use this, on the producer side the ipw2100 driver is patched.

A generic maximum latency is also registered of 2 timer ticks (more and you
lose accurate time tracking after all).

While the existing users of the patch are x86 specific, the infrastructure
is not.  I'd like to ask the arch maintainers of other architectures if the
infrastructure is generic enough for their use (assuming the architecture
has such a tradeoff as concept at all), and the sound/multimedia driver
owners to look at the driver facing API to see if this is something they
can use.

[akpm@osdl.org: cleanups]
Signed-off-by: Arjan van de Ven 
Signed-off-by: Ingo Molnar 
Acked-by: Jesse Barnes 
Cc: "Brown, Len" 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds