Message-ID: <819d8fa2-b73e-e32f-5442-452aa2c0d752@bytedance.com>
Date:   Sun, 26 Feb 2023 20:59:17 +0000
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Subject: Re: [External] Re: [PATCH v12 00/11] Parallel CPU bringup for x86_64
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To:     Oleksandr Natalenko <oleksandr@natalenko.name>,
        dwmw2@infradead.org, tglx@linutronix.de, kim.phillips@amd.com,
        brgerst@gmail.com
Cc:     piotrgorski@cachyos.org, arjan@linux.intel.com, mingo@redhat.com,
        bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com,
        x86@kernel.org, pbonzini@redhat.com, paulmck@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        rcu@vger.kernel.org, mimoja@mimoja.de, hewenliang4@huawei.com,
        thomas.lendacky@amd.com, seanjc@google.com, pmenzel@molgen.mpg.de,
        fam.zheng@bytedance.com, punit.agrawal@bytedance.com,
        simon.evans@bytedance.com, liangma@liangbit.com
References: <20230226110802.103134-1-usama.arif@bytedance.com>
 <5650744.DvuYhMxLoT@natalenko.name>
From:   Usama Arif <usama.arif@bytedance.com>
In-Reply-To: <5650744.DvuYhMxLoT@natalenko.name>
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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?

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index c2aa0aa26b45..e3727dab9cab 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -35,7 +35,7 @@ typedef struct cpumask { DECLARE_BITMAP(bits, 
NR_CPUS); } cpumask_t;
   */
  #define cpumask_pr_args(maskp)         nr_cpu_ids, cpumask_bits(maskp)

-#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)
+#if ((NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)) && 
!defined(CONFIG_SMP)
  #define nr_cpu_ids ((unsigned int)NR_CPUS)
  #else
  extern unsigned int nr_cpu_ids;
@@ -43,7 +43,7 @@ extern unsigned int nr_cpu_ids;

  static inline void set_nr_cpu_ids(unsigned int nr)
  {
-#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)
+#if ((NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)) && 
!defined(CONFIG_SMP)
         WARN_ON(nr != nr_cpu_ids);
  #else
         nr_cpu_ids = nr;
diff --git a/kernel/smp.c b/kernel/smp.c
index 06a413987a14..a051b16d4a24 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -1087,11 +1087,9 @@ static int __init maxcpus(char *str)

  early_param("maxcpus", maxcpus);

-#if (NR_CPUS > 1) && !defined(CONFIG_FORCE_NR_CPUS)
  /* Setup number of possible processor ids */
  unsigned int nr_cpu_ids __read_mostly = NR_CPUS;
  EXPORT_SYMBOL(nr_cpu_ids);
-#endif

  /* An arch may set nr_cpu_ids earlier if needed, so this would be 
redundant */
  void __init setup_nr_cpu_ids(void)