linux-kernel - Re: [PATCH 01/10] x86: Add topology_max_smt

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Message-ID: <20160506101318.GV3430@twins.programming.kicks-ass.net>
Date:	Fri, 6 May 2016 12:13:18 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	acme@...nel.org, jolsa@...nel.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Subject: Re: [PATCH 01/10] x86: Add topology_max_smt_threads()


It might help if you actually Cc'd tglx and x86 in general.

On Thu, May 05, 2016 at 04:03:58PM -0700, Andi Kleen wrote:
> From: Andi Kleen <ak@...ux.intel.com>
> 
> For SMT specific workarounds it is useful to know if SMT is active
> on any online CPU in the system. This currently requires a loop
> over all online CPUs.
> 
> Add a global variable that is updated with the maximum number
> of smt threads on any CPU on online/offline, and use it for
> topology_max_smt_threads()
> 
> The single call is easier to use than a loop.
> 
> Not exported to user space because user space already can use
> the existing sibling interfaces to find this out.
> 
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> ---
>  arch/x86/include/asm/topology.h |  5 +++++
>  arch/x86/kernel/smpboot.c       | 24 ++++++++++++++++++++++++
>  2 files changed, 29 insertions(+)
> 
> diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
> index 7f991bd5031b..4707555f209e 100644
> --- a/arch/x86/include/asm/topology.h
> +++ b/arch/x86/include/asm/topology.h
> @@ -129,6 +129,10 @@ extern const struct cpumask *cpu_coregroup_mask(int cpu);
>  
>  extern unsigned int __max_logical_packages;
>  #define topology_max_packages()			(__max_logical_packages)
> +
> +extern int max_smt_threads;
> +#define topology_max_smt_threads()		max_smt_threads
> +
>  int topology_update_package_map(unsigned int apicid, unsigned int cpu);
>  extern int topology_phys_to_logical_pkg(unsigned int pkg);
>  #else
> @@ -136,6 +140,7 @@ extern int topology_phys_to_logical_pkg(unsigned int pkg);
>  static inline int
>  topology_update_package_map(unsigned int apicid, unsigned int cpu) { return 0; }
>  static inline int topology_phys_to_logical_pkg(unsigned int pkg) { return 0; }
> +#define topology_max_smt_threads()		1
>  #endif
>  
>  static inline void arch_fix_phys_package_id(int num, u32 slot)
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index a2065d3b3b39..6e5a721857f5 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -105,6 +105,9 @@ static unsigned int max_physical_pkg_id __read_mostly;
>  unsigned int __max_logical_packages __read_mostly;
>  EXPORT_SYMBOL(__max_logical_packages);
>  
> +/* Maximum number of SMT threads on any online core */
> +int max_smt_threads __read_mostly;
> +
>  static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
>  {
>  	unsigned long flags;
> @@ -489,6 +492,7 @@ void set_cpu_sibling_map(int cpu)
>  	struct cpuinfo_x86 *c = &cpu_data(cpu);
>  	struct cpuinfo_x86 *o;
>  	int i;
> +	int threads;
>  
>  	cpumask_set_cpu(cpu, cpu_sibling_setup_mask);
>  
> @@ -545,6 +549,10 @@ void set_cpu_sibling_map(int cpu)
>  		if (match_die(c, o) && !topology_same_node(c, o))
>  			primarily_use_numa_for_topology();
>  	}
> +
> +	threads = cpumask_weight(topology_sibling_cpumask(cpu));
> +	if (threads > max_smt_threads)
> +		max_smt_threads = threads;
>  }
>  
>  /* maps the cpu to the sched domain representing multi-core */
> @@ -1436,6 +1444,21 @@ __init void prefill_possible_map(void)
>  
>  #ifdef CONFIG_HOTPLUG_CPU
>  
> +/* Recompute SMT state for all CPUs on offline */
> +static void recompute_smt_state(void)
> +{
> +	int max_threads;
> +	int cpu;
> +
> +	max_threads = 0;
> +	for_each_online_cpu (cpu) {
> +		int threads = cpumask_weight(topology_sibling_cpumask(cpu));
> +		if (threads > max_threads)
> +			max_threads = threads;
> +	}
> +	max_smt_threads = max_threads;
> +}
> +
>  static void remove_siblinginfo(int cpu)
>  {
>  	int sibling;
> @@ -1460,6 +1483,7 @@ static void remove_siblinginfo(int cpu)
>  	c->phys_proc_id = 0;
>  	c->cpu_core_id = 0;
>  	cpumask_clear_cpu(cpu, cpu_sibling_setup_mask);
> +	recompute_smt_state();
>  }
>  
>  static void remove_cpu_from_maps(int cpu)
> -- 
> 2.5.5
>