linux-kernel - Re: [PATCH] arch/x86: Remove second call to topology_update_package

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Date:   Wed, 12 Oct 2016 11:06:25 -0400
From:   Prarit Bhargava <prarit@...hat.com>
To:     linux-kernel@...r.kernel.org
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Len Brown <len.brown@...el.com>, Borislav Petkov <bp@...e.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH] arch/x86: Remove second call to topology_update_package_map()



On 10/12/2016 10:36 AM, Prarit Bhargava wrote:
> This was noticed during the investigation of
> 
> http://git.kernel.org/tip/2a51fe083eba7f99cbda72f5ef90cdf2f4df882c
> 
> A note for reviewers on the cleanup in smp_init_package_map(): The
> per_cpu variable x86_bios_cpu_apicid is initialized to BAD_APICID, and the
> bitmaps are set to false by default so the code isn't necessary.  The
> pr_warn() can also be dropped as generic_processor_info() will do a
> pr_warning() in the same situation.


> 
> P.
> 
> -----8<-----
> 
> After commit 1f12e32f4cd5 ("x86/topology: Create logical package id"),
> topology_update_package_map() is called twice on a CPU.  The first call is in
> generic_processor_info(), which is called on all present cpus (found in either
> mptable or ACPI MADT).  The second call is in smp_init_package_map() which
> is called later on in the init sequence.
> 
> Only a single call is necessary for the kernel to initialize the data
> structures properly. This patch drops the later call in smp_init_package_map()
> and moves smp_init_package_map() out of smp_store_boot_cpu_info().
> 

Self-NAK.

This seems to not work on systems with an empty socket :/.  Looking into this now.

P.

> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: x86@...nel.org
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> Cc: Andi Kleen <ak@...ux.intel.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> ---
>  arch/x86/kernel/smpboot.c |   20 +++-----------------
>  1 file changed, 3 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 951f093a96fe..0ff74f8bb5e9 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -271,7 +271,7 @@ int topology_update_package_map(unsigned int apicid, unsigned int cpu)
>  	if (!physical_package_map)
>  		return 0;
>  
> -	if (pkg >= max_physical_pkg_id)
> +	if (!apic->apic_id_valid(apicid) || pkg >= max_physical_pkg_id)
>  		return -EINVAL;
>  
>  	/* Set the logical package id */
> @@ -310,7 +310,7 @@ int topology_phys_to_logical_pkg(unsigned int phys_pkg)
>  
>  static void __init smp_init_package_map(void)
>  {
> -	unsigned int ncpus, cpu;
> +	unsigned int ncpus;
>  	size_t size;
>  
>  	/*
> @@ -342,7 +342,6 @@ static void __init smp_init_package_map(void)
>  	}
>  
>  	__max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);
> -	logical_packages = 0;
>  
>  	/*
>  	 * Possibly larger than what we need as the number of apic ids per
> @@ -355,19 +354,6 @@ static void __init smp_init_package_map(void)
>  	size = BITS_TO_LONGS(max_physical_pkg_id) * sizeof(unsigned long);
>  	physical_package_map = kzalloc(size, GFP_KERNEL);
>  
> -	for_each_present_cpu(cpu) {
> -		unsigned int apicid = apic->cpu_present_to_apicid(cpu);
> -
> -		if (apicid == BAD_APICID || !apic->apic_id_valid(apicid))
> -			continue;
> -		if (!topology_update_package_map(apicid, cpu))
> -			continue;
> -		pr_warn("CPU %u APICId %x disabled\n", cpu, apicid);
> -		per_cpu(x86_bios_cpu_apicid, cpu) = BAD_APICID;
> -		set_cpu_possible(cpu, false);
> -		set_cpu_present(cpu, false);
> -	}
> -
>  	if (logical_packages > __max_logical_packages) {
>  		pr_warn("Detected more packages (%u), then computed by BIOS data (%u).\n",
>  			logical_packages, __max_logical_packages);
> @@ -385,7 +371,6 @@ void __init smp_store_boot_cpu_info(void)
>  
>  	*c = boot_cpu_data;
>  	c->cpu_index = id;
> -	smp_init_package_map();
>  }
>  
>  /*
> @@ -1285,6 +1270,7 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
>  	 * Setup boot CPU information
>  	 */
>  	smp_store_boot_cpu_info(); /* Final full version of the data */
> +	smp_init_package_map();
>  	cpumask_copy(cpu_callin_mask, cpumask_of(0));
>  	mb();
>  
>