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Date: Mon, 27 Feb 2023 06:14:00 +0000
From: Usama Arif <usama.arif@...edance.com>
To: Oleksandr Natalenko <oleksandr@...alenko.name>,
dwmw2@...radead.org, 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 26/02/2023 20:59, Usama Arif 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?
>
> 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)
Or better just do below?
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 17bdd6122dca..5d709aa67df4 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -273,7 +273,11 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify,
SYM_L_GLOBAL)
cmpl (%rbx,%rcx,4), %edx
jz .Lsetup_cpu
inc %ecx
+#if (NR_CPUS == 1) || defined(CONFIG_FORCE_NR_CPUS)
+ cmpl $NR_CPUS, %ecx
+#else
cmpl nr_cpu_ids(%rip), %ecx
+#endif
jb .Lfind_cpunr
/* APIC ID not found in the table. Drop the trampoline lock
and bail. */
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