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Message-ID: <EB27C1C4-7246-4557-A6B3-EBBC9E8FC69F@infradead.org>
Date: Mon, 27 Feb 2023 06:13:22 +0000
From: David Woodhouse <dwmw2@...radead.org>
To: Usama Arif <usama.arif@...edance.com>,
Oleksandr Natalenko <oleksandr@...alenko.name>,
tglx@...utronix.de, kim.phillips@....com, brgerst@...il.com
CC: piotrgorski@...hyos.org, arjan@...ux.intel.com, mingo@...hat.com,
bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
x86@...nel.org, pbonzini@...hat.com, paulmck@...nel.org,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
rcu@...r.kernel.org, mimoja@...oja.de, hewenliang4@...wei.com,
thomas.lendacky@....com, seanjc@...gle.com, pmenzel@...gen.mpg.de,
fam.zheng@...edance.com, punit.agrawal@...edance.com,
simon.evans@...edance.com, liangma@...ngbit.com
Subject: Re: [External] Re: [PATCH v12 00/11] Parallel CPU bringup for x86_64
On 26 February 2023 20:59:17 GMT, Usama Arif <usama.arif@...edance.com> 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@gmail.com/).
>>> 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.
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