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

Usama Arif
2023-02-26T20:59:55Z

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)