[RFC PATCH v2 00/12] Unify interrupt mode and setup it as soon as possible

[Dou Liyang]

According to Ingo's and Eric's advice[1,2], Try my best to optimize the 
init of interrupt delivery mode for x86.

MP specification defines three different interrupt modes as follows:

 1. PIC Mode
 2. Virtual Wire Mode
 3. Symmetric I/O Mode

Currently, in kernel,

1. Setup Virtual Wire Mode during IRQ initialization( step 1
in the following figure).

2. Enable and Setup Symmetric I/O Mode either during the
SMP-capable system prepares CPUs(step 2) or during the UP system 
initializes itself(step 3).

  start_kernel
+---------------+
|
+--> .......
|
|    setup_arch
+--> +-------+
|
|    init_IRQ
+-> +--+-----+
|      |        init_ISA_irqs
|      +------> +-+--------+
|                 |         +----------------+
+--->             +------>  | 1.init_bsp_APIC|
|     .......               +----------------+
+--->
|     rest_init
+--->---+-----+
|       |   kernel_init
|       +> ----+-----+
|              |   kernel_init_freeable
|              +->  ----+-------------+
|                       |     smp_prepare_cpus
|                       +---> +----+---------+
|                       |          |   +-------------------+
|                       |          +-> |2.  apic_bsp_setup |
|                       |              +-------------------+
|                       |
v                       |     smp_init
                        +---> +---+----+
                                  |    +-------------------+
                                  +--> |3.  apic_bsp_setup |
                                       +-------------------+

The purpose of this patchset is unifying these setup steps and executing
as soon as possible as follows:

   start_kernel
---------------+
|
|
|
|    x86_late_time_init
+---->---+------------+
|        |
|        |      +------------------------+
|        +----> | 4. init_interrupt_mode |
|               +------------------------+
v

By the way, Also fix a bug about kexec[3].

[1]. https://lkml.org/lkml/2016/8/2/929
[2]. https://lkml.org/lkml/2016/8/1/506
[3]. https://lkml.org/lkml/2016/7/25/1118

Changes since V1:

  - Move the initialization from init_IRQ() to x86_late_time_init()
  - Use a threshold to refactor the check logic in timer_irq_works()
  - Rename the framework to a selector
  - Split two patches
  - Consistently start sentences with upper case letters
  - Fix some typos
  - Rewrite the changelog

Dou Liyang (12):
  x86/apic: Replace init_bsp_APIC() with apic_virtual_wire_mode_setup()
  x86/apic: Construct a selector for the interrupt delivery mode
  x86/apic: Prepare for unifying the interrupt delivery modes setup
  x86/time: Initialize interrupt mode behind timer init
  x86/ioapic: Refactor the delay logic in timer_irq_works()
  x86/apic: Split local APIC timer setup from the APIC setup
  x86/apic: Move the logical APIC ID setup from apic_bsp_setup()
  x86/apic: Make the interrupt mode setup earlier for SMP-capable system
  x86/apic: Setup interrupt mode earlier in case of no SMP motherboard
  x86/apic: Make the interrupt mode setup earlier for UP system
  x86/apic: Mark the apic_interrupt_mode extern for refining code
  x86/apic: Remove the apic_virtual_wire_mode_setup()

 arch/x86/include/asm/apic.h    |  14 +++-
 arch/x86/kernel/apic/apic.c    | 183 +++++++++++++++++++++--------------------
 arch/x86/kernel/apic/io_apic.c |  47 +++++++++--
 arch/x86/kernel/irqinit.c      |   3 -
 arch/x86/kernel/smpboot.c      |  64 +++-----------
 arch/x86/kernel/time.c         |   8 ++
 6 files changed, 168 insertions(+), 151 deletions(-)

-- 
2.5.5