According to Ingo's and Eric's advice[1,2], Try my best to optimize the init of Interrupt Mode for x86.
The MP specification defines three different interrupt modes as follows: 1. PIC Mode 2. Virtual Wire Mode 3. Symmetic I/O Mode Currently, In kernel, 1. Setup the Virtual Wire Mode during the IRQ initialization( step 1 in the following figure). 2. Enable and Setup the Symmetic I/O Mode either during the SMP-capabe 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 Unifing these setup steps and executing as soon as possible as follows: start_kernel ---------------+ | | | | init_IRQ +---->---+----+ | | | | +--------------------+ | +----> | 4. init_bsp_APIC | | +--------------------+ v By the way, Also fix a bug about kexec[3]. Some doubts, need help: 1. Patchset has influence on IOMMU in enable_IR_x2apic(). Not sure it can be in advance? 2. Due to Commit 8c3ba8d04924 ("x86, apic: ack all pending irqs when crashed/on kexec") ..., patchset also needs TSC and uses the "cpu_khz" in setup_local_APIC(). And a warning[4] will be triggered when crashed/on kexec. Not sure how to modify? [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 [4]. WARN_ON(max_loops <= 0) in setup_local_APIC() Dou Liyang (6): x86/apic: Replace init_bsp_APIC() with apic_virture_wire_mode_setup() x86/apic: Construct a framework for setuping APIC mode as soon as possible x86/apic: Extract APIC timer related code from apic_bsp_setup() x86/apic: Make the APIC mode setup earlier for SMP-capable system x86/apic: Make the APIC mode setup earlier for UP system x86/apic: Remove the apic_virture_wire_mode_setup() arch/x86/include/asm/apic.h | 7 +- arch/x86/include/asm/io_apic.h | 2 + arch/x86/kernel/apic/apic.c | 218 ++++++++++++++++++++++++----------------- arch/x86/kernel/apic/io_apic.c | 4 +- arch/x86/kernel/irqinit.c | 6 +- arch/x86/kernel/smpboot.c | 68 ++----------- 6 files changed, 149 insertions(+), 156 deletions(-) -- 2.5.5