linux-kernel - Re: [External] Re: [PATCH v8 6/9] x86/smpboot: Support parallel startup of secondary CPUs

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Date:   Thu, 9 Feb 2023 20:37:58 +0000
From:   Usama Arif <usama.arif@...edance.com>
To:     Thomas Gleixner <tglx@...utronix.de>, dwmw2@...radead.org,
        kim.phillips@....com
Cc:     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,
        David Woodhouse <dwmw@...zon.co.uk>
Subject: Re: [External] Re: [PATCH v8 6/9] x86/smpboot: Support parallel
 startup of secondary CPUs



On 09/02/2023 18:25, Thomas Gleixner wrote:
> On Thu, Feb 09 2023 at 15:41, Usama Arif wrote:
>>   
>> +static bool do_parallel_bringup = true;
> 
> Wants to be __ro_after_init
> 
>> +static int __init no_parallel_bringup(char *str)
>> +{
>> +	do_parallel_bringup = false;
>> +
>> +	return 0;
>> +}
>> +early_param("no_parallel_bringup", no_parallel_bringup);
> 
> Lacks an entry in Documentation/admin/kernel-parameters.txt
> 
> Thanks,
> 
>          tglx


Thanks, I will add the below to next revision. Its quite minor so will 
wait for more comments and MTRR question to be resolved, unless told to 
send next revision with this diff only.

diff --git a/Documentation/admin-guide/kernel-parameters.txt 
b/Documentation/admin-guide/kernel-parameters.txt
index 6cfa6e3996cf..d3696c9316f1 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3830,6 +3830,9 @@
         noreplace-smp   [X86-32,SMP] Don't replace SMP instructions
                         with UP alternatives

+       no_parallel_bringup
+                       [X86,SMP] Disables parallel brinugp of secondary 
cores.
+
         noresume        [SWSUSP] Disables resume and restores original swap
                         space.

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 3ec5182d9698..fecd934e72fb 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -813,7 +813,7 @@ static int __init cpu_init_udelay(char *str)
  }
  early_param("cpu_init_udelay", cpu_init_udelay);

-static bool do_parallel_bringup = true;
+static bool do_parallel_bringup __ro_after_init = true;

  static int __init no_parallel_bringup(char *str)
  {