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Subject[RFC PATCH v3 00/12] Unify interrupt mode and setup it as soon as possible
Date
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 patches is unifying these setup steps and executing
as soon as possible as follows:

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

And construct a selector to wrap all the switches and make them
maintain and read easily.

Original:

+-----------------------------------------------------+
| smp_found_config || !boot_cpu_has(X86_FEATURE_APIC) |
+-----------------------------------------------------+
|true, PIC MODE |false, VIRTUAL WIRE MODE
| |
+--v-----------------v-----------+
|!smp_found_config && !acpi_lapic+-----+
+--------------------------------+ |
|false |
| |
+--v----------------------------+ |
|!boot_cpu_has(X86_FEATURE_APIC)+ true |
+------------------+------------+ |
|false | |
v | +------v-----+ true
SYMMETRIC IO MODE | |disable_apic+------> PIC MODE
| +------------+
|true |false
| +---v---------------------------+
+------v------+ |!boot_cpu_has(X86_FEATURE_APIC)|
|!disable_apic| +---------------------------+---+
+------+------+ |false |true
| +----v------------+ v
v |!smp_found_config+----+ PIC MODE
PIC MODE +-----------------+ |
|false |true
v v
SYMMETRIC IO MODE VIRTUAL WIRE MODE
Now:

+------------+
|disable_apic+--------------------+
+------------+ true |
|false |
| |
+------------v------------------+ |
|!boot_cpu_has(X86_FEATURE_APIC)+-------+
+-------------------------------+ true |
|false |
| |
+-------v---------+ v
|!smp_found_config| PIC MODE
+---------------+-+
|false |true
| |
v +---v---------+
SYMMETRIC IO MODE | !acpi_lapic |
+------+------+
|
v
VIRTUAL WIRE MODE

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 V2 --> V3:

- Rebase the patches.
- Change two function name:
apic_bsp_mode_check --> apic_interrupt_mode_select
init_interrupt_mode --> apic_interrupt_mode_init
- Find a new waiting way to check whether timer IRQs work or not
- Refine the switch logic in apic_interrupt_mode_init()
- Consistently start sentences with upper case letters
- Fix some typos and comments
- Try my best to rewrite some changelog again

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 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 disable_smp()
x86/apic: Remove the apic_virtual_wire_mode_setup()

arch/x86/include/asm/apic.h | 15 +++-
arch/x86/kernel/apic/apic.c | 185 +++++++++++++++++++++--------------------
arch/x86/kernel/apic/io_apic.c | 46 +++++++++-
arch/x86/kernel/irqinit.c | 3 -
arch/x86/kernel/smpboot.c | 65 ++++-----------
arch/x86/kernel/time.c | 8 ++
6 files changed, 174 insertions(+), 148 deletions(-)

--
2.5.5



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