[PATCH 0/9] Parallel CPU bringup for x86_64

[Usama Arif <usama.arif@bytedance.com>]

This patchseries is from the work done by David Woodhouse (v4: https://lore.kernel.org/all/20220201205328.123066-1-dwmw2@infradead.org/).
The parallel CPU bringup is disabled for all AMD CPUs in this version: (see discussions: https://lore.kernel.org/all/bc3f2b1332c4bb77558df8aa36493a55542fe5b9.camel@infradead.org/ and
https://lore.kernel.org/all/3b6ac86fdc800cac5806433daf14a9095be101e9.camel@infradead.org/).

Doing INIT/SIPI/SIPI in parallel brings down the time for smpboot from ~700ms
to 100ms (85% improvement) on a server with 128 CPUs split across 2 NUMA
nodes.

Adding another cpuhp state for do_wait_cpu_initialized to make sure cpu_init
is reached in parallel as proposed by David in v1 will bring it down further
to ~30ms. Making this change would be dependent on this patchseries, so they
could be explored if this gets merged.

Changes across versions:
v2: Cut it back to just INIT/SIPI/SIPI in parallel for now, nothing more
v3: Clean up x2apic patch, add MTRR optimisation, lock topology update
    in preparation for more parallelisation.
v4: Fixes to the real mode parallelisation patch spotted by SeanC, to
    avoid scribbling on initial_gs in common_cpu_up(), and to allow all
    24 bits of the physical X2APIC ID to be used. That patch still needs
    a Signed-off-by from its original author, who once claimed not to
    remember writing it at all. But now we've fixed it, hopefully he'll
    admit it now :)
v5: rebase to v6.1 and remeasure performance, disable parallel bringup
    for AMD CPUs.

David Woodhouse (8):
  x86/apic/x2apic: Fix parallel handling of cluster_mask
  cpu/hotplug: Move idle_thread_get() to <linux/smpboot.h>
  cpu/hotplug: Add dynamic parallel bringup states before
    CPUHP_BRINGUP_CPU
  x86/smpboot: Reference count on smpboot_setup_warm_reset_vector()
  x86/smpboot: Split up native_cpu_up into separate phases and document
    them
  x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel
  x86/mtrr: Avoid repeated save of MTRRs on boot-time CPU bringup
  x86/smpboot: Serialize topology updates for secondary bringup

Thomas Gleixner (1):
  x86/smpboot: Support parallel startup of secondary CPUs

 arch/x86/include/asm/realmode.h       |   3 +
 arch/x86/include/asm/smp.h            |  13 +-
 arch/x86/include/asm/topology.h       |   2 -
 arch/x86/kernel/acpi/sleep.c          |   1 +
 arch/x86/kernel/apic/apic.c           |   2 +-
 arch/x86/kernel/apic/x2apic_cluster.c | 108 +++++----
 arch/x86/kernel/cpu/common.c          |   6 +-
 arch/x86/kernel/cpu/mtrr/mtrr.c       |   9 +
 arch/x86/kernel/head_64.S             |  73 ++++++
 arch/x86/kernel/smpboot.c             | 324 ++++++++++++++++++--------
 arch/x86/realmode/init.c              |   3 +
 arch/x86/realmode/rm/trampoline_64.S  |  14 ++
 arch/x86/xen/smp_pv.c                 |   4 +-
 include/linux/cpuhotplug.h            |   2 +
 include/linux/smpboot.h               |   7 +
 kernel/cpu.c                          |  27 ++-
 kernel/smpboot.c                      |   2 +-
 kernel/smpboot.h                      |   2 -
 18 files changed, 443 insertions(+), 159 deletions(-)

-- 
2.25.1