Re: [External] Re: [PATCH v12 00/11] Parallel CPU bringup for x86_64

[David Woodhouse]

On 26 February 2023 20:59:17 GMT, Usama Arif <usama.arif@xxxxxxxxxxxxx> wrote:
>
>
>On 26/02/2023 18:31, Oleksandr Natalenko wrote:
>> Hello.
>> 
>> On neděle 26. února 2023 12:07:51 CET Usama Arif wrote:
>>> The main code change over v11 is the build error fix by Brian Gerst and
>>> acquiring tr_lock in trampoline_64.S whenever the stack is setup.
>>> 
>>> The git history is also rewritten to move the commits that removed
>>> initial_stack, early_gdt_descr and initial_gs earlier in the patchset.
>>> 
>>> Thanks,
>>> Usama
>>> 
>>> 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.
>>> v6: rebase to v6.2-rc6, disabled parallel boot on amd as a cpu bug and
>>>      reused timer calibration for secondary CPUs.
>>> v7: [David Woodhouse] iterate over all possible CPUs to find any existing
>>>      cluster mask in alloc_clustermask. (patch 1/9)
>>>      Keep parallel AMD support enabled in AMD, using APIC ID in CPUID leaf
>>>      0x0B (for x2APIC mode) or CPUID leaf 0x01 where 8 bits are sufficient.
>>>      Included sanity checks for APIC id from 0x0B. (patch 6/9)
>>>      Removed patch for reusing timer calibration for secondary CPUs.
>>>      commit message and code improvements.
>>> v8: Fix CPU0 hotplug by setting up the initial_gs, initial_stack and
>>>      early_gdt_descr.
>>>      Drop trampoline lock and bail if APIC ID not found in find_cpunr.
>>>      Code comments improved and debug prints added.
>>> v9: Drop patch to avoid repeated saves of MTRR at boot time.
>>>      rebased and retested at v6.2-rc8.
>>>      added kernel doc for no_parallel_bringup and made do_parallel_bringup
>>>      __ro_after_init.
>>> v10: Fixed suspend/resume not working with parallel smpboot.
>>>       rebased and retested to 6.2.
>>>       fixed checkpatch errors.
>>> v11: Added patches from Brian Gerst to remove the global variables initial_gs,
>>>       initial_stack, and early_gdt_descr from the 64-bit boot code
>>>       (https://lore.kernel.org/all/20230222221301.245890-1-brgerst@xxxxxxxxx/).
>>> v12: Fixed compilation errors, acquire tr_lock for every stack setup in
>>>       trampoline_64.S.
>>>       Rearranged commits for a cleaner git history.
>>> 
>>> Brian Gerst (3):
>>>    x86/smpboot: Remove initial_stack on 64-bit
>>>    x86/smpboot: Remove early_gdt_descr on 64-bit
>>>    x86/smpboot: Remove initial_gs
>>> 
>>> David Woodhouse (8):
>>>    x86/apic/x2apic: Allow CPU cluster_mask to be populated in parallel
>>>    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: Support parallel startup of secondary CPUs
>>>    x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel
>>>    x86/smpboot: Serialize topology updates for secondary bringup
>>> 
>>>   .../admin-guide/kernel-parameters.txt         |   3 +
>>>   arch/x86/include/asm/processor.h              |   6 +-
>>>   arch/x86/include/asm/realmode.h               |   4 +-
>>>   arch/x86/include/asm/smp.h                    |  15 +-
>>>   arch/x86/include/asm/topology.h               |   2 -
>>>   arch/x86/kernel/acpi/sleep.c                  |  15 +-
>>>   arch/x86/kernel/apic/apic.c                   |   2 +-
>>>   arch/x86/kernel/apic/x2apic_cluster.c         | 126 ++++---
>>>   arch/x86/kernel/asm-offsets.c                 |   1 +
>>>   arch/x86/kernel/cpu/common.c                  |   6 +-
>>>   arch/x86/kernel/head_64.S                     | 129 +++++--
>>>   arch/x86/kernel/smpboot.c                     | 350 +++++++++++++-----
>>>   arch/x86/realmode/init.c                      |   3 +
>>>   arch/x86/realmode/rm/trampoline_64.S          |  27 +-
>>>   arch/x86/xen/smp_pv.c                         |   4 +-
>>>   arch/x86/xen/xen-head.S                       |   2 +-
>>>   include/linux/cpuhotplug.h                    |   2 +
>>>   include/linux/smpboot.h                       |   7 +
>>>   kernel/cpu.c                                  |  31 +-
>>>   kernel/smpboot.h                              |   2 -
>>>   20 files changed, 537 insertions(+), 200 deletions(-)
>> 
>> With `CONFIG_FORCE_NR_CPUS=y` this results in:
>> 
>> ```
>> ld: vmlinux.o: in function `secondary_startup_64_no_verify':
>> (.head.text+0x10c): undefined reference to `nr_cpu_ids'
>> ```
>> 
>> That's because in `arch/x86/kernel/head_64.S` `secondary_startup_64_no_verify()` refers to `nr_cpu_ids` under `#ifdef CONFIG_SMP`, but this symbol is available under the following conditions:
>> 
>> ```
>> 38 #if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)
>> 39 #define nr_cpu_ids ((unsigned int)NR_CPUS)
>> 40 #else
>> 41 extern unsigned int nr_cpu_ids;
>> 42 #endif
>> 
>> 1090 #if (NR_CPUS > 1) && !defined(CONFIG_FORCE_NR_CPUS)
>> 1091 /* Setup number of possible processor ids */
>> 1092 unsigned int nr_cpu_ids __read_mostly = NR_CPUS;
>> 1093 EXPORT_SYMBOL(nr_cpu_ids);
>> 1094 #endif
>> ```
>> 
>> So having `CONFIG_SMP=y` and, for instance, `CONFIG_NR_CPUS=320`, it is possible to compile out `EXPORT_SYMBOL(nr_cpu_ids);` if `CONFIG_FORCE_NR_CPUS=y` is set.
>> 
>
>I think something like below diff should work in all scenarios?

I'd've changed the asm side to use the constant limit.