linux-kernel - Re: [PATCH 1/2] perf-events: Add support for supplementary event registers v2

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Message-ID: <1289582265.2084.328.camel@laptop>
Date:	Fri, 12 Nov 2010 18:17:45 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	eranian@...gle.com, linux-kernel@...r.kernel.org,
	cjashfor@...ux.vnet.ibm.com, mingo@...e.hu, fweisbec@...il.com,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 1/2] perf-events: Add support for supplementary event
 registers v2

On Fri, 2010-11-12 at 17:55 +0100, Andi Kleen wrote:

> @@ -127,6 +129,13 @@ struct cpu_hw_events {
>  	struct perf_branch_stack	lbr_stack;
>  	struct perf_branch_entry	lbr_entries[MAX_LBR_ENTRIES];
>  
> +	/* 
> +	 * Intel percore register state.
> +	 * Coordinate shared resources between HT threads.
> +	 */
> +	int 				percore_used; /* Used by this CPU? */
> +	struct intel_percore		*per_core;
> +
>  	/*
>  	 * AMD specific bits
>  	 */

> +/* 
> + * Per core state
> + * This used to coordinate shared resources for HT threads.
> + * Exists per CPU, but only the entry for the first CPU
> + * in the core is used.
> + */
> +struct intel_percore {
> +	raw_spinlock_t 		lock;		/* protect structure */
> +	int 			ref;		/* reference count */
> +	u64 			config;	        /* main counter config */
> +	unsigned int 		extra_reg;	/* extra MSR number */
> +	u64 			extra_config;	/* extra MSR config */
> +};
> +static struct intel_percore __percpu *intel_percore;

Why have this pointer?

> @@ -923,6 +1045,35 @@ static void intel_clovertown_quirks(void)
>  	x86_pmu.pebs_constraints = NULL;
>  }
>  
> +static __initdata int needs_percore = 1; /* CHANGEME */
> +
> +static __init int init_intel_percore(void)
> +{
> +	int cpu;
> +
> +	if (!needs_percore)
> +		return 0;
> +
> +	intel_percore = alloc_percpu(struct intel_percore);
> +	if (!intel_percore)
> +		return -ENOMEM;
> +
> +	for_each_possible_cpu(cpu) {
> +		raw_spin_lock_init(&per_cpu_ptr(intel_percore, cpu)->lock);
> +		per_cpu(cpu_hw_events, cpu).per_core =
> +			per_cpu_ptr(intel_percore,
> +			    cpumask_first(topology_thread_cpumask(cpu)));
> +		printk("cpu %d core %d\n", 
> +		       cpu, cpumask_first(topology_thread_cpumask(cpu)));
> +	}
> +
> +	return 0;
> +}
> +/* 
> + * Runs later because per cpu allocations don't work early on.
> + */
> +__initcall(init_intel_percore);

they should, perf is initialized from sched_init() [ I really should
move it into init/main.c some time ], which is after mm_init(), which
should be sufficient for all allocators to work.

Oh, wait, I ran into this a few days ago, the arch specific init call
actually runs before the main perf init, which is mightly strange, I
have this hunk (http://lkml.org/lkml/2010/11/9/530):

-void __init init_hw_perf_events(void)
+static int __init init_hw_perf_events(void)
 {
 	struct event_constraint *c;
 	int err;
@@ -1363,11 +1363,11 @@ void __init init_hw_perf_events(void)
 		err = amd_pmu_init();
 		break;
 	default:
-		return;
+		return 0;
 	}
 	if (err != 0) {
 		pr_cont("no PMU driver, software events only.\n");
-		return;
+		return 0;
 	}
 
 	pmu_check_apic();
@@ -1418,9 +1418,12 @@ void __init init_hw_perf_events(void)
 	pr_info("... fixed-purpose events:   %d\n",     x86_pmu.num_counters_fixed);
 	pr_info("... event mask:             %016Lx\n", x86_pmu.intel_ctrl);
 
	perf_pmu_register(&pmu);
 	perf_cpu_notifier(x86_pmu_notifier);
+
+	return 0;
 }
+early_initcall(init_hw_perf_events);

To cure that.


That said, why not simply:
  kmalloc_node(sizeof(struct intel_percore)), GFP_KERNEL | __GFP_ZERO, 
	       cpu_to_node(cpu))

For each core, just like amd_alloc_nb() does. The amd code even frees
the allocation on cpu-hot-unplug of after all relevant cpus are gone.

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