linux-kernel - Re: [PATCH 4/7] perf: Check if HT is supported and enabled

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Date:	Tue, 28 Dec 2010 16:51:28 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	Stephane Eranian <eranian@...gle.com>,
	lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/7] perf: Check if HT is supported and enabled

On Tue, 2010-12-28 at 16:44 +0800, Lin Ming wrote:
> 
> Avoid the percore allocations if HT is not supported or disabled.
> 
> Signed-off-by: Lin Ming <ming.m.lin@...el.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel.c |   44 +++++++++++++++++++++++++++----
>  1 files changed, 38 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/perf_event_intel.c
> b/arch/x86/kernel/cpu/perf_event_intel.c
> index bc4afb1..354d1de 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel.c
> @@ -1053,9 +1053,38 @@ static __initconst const struct x86_pmu core_pmu = {
>        .event_constraints      = intel_core_event_constraints,
>  };
> 
> +/*
> + * Check if HT is capable and enabled
> + * TBD: move it to generic place, so it can be used by others
> + */
> +
> +static bool ht_enabled(int cpu)
> +{
> +       int total_logical_processors, total_cores;
> +       unsigned int eax, ebx, ecx, edx;
> +
> +       cpuid(1, &eax, &ebx, &ecx, &edx);
> +
> +       /* Bit 28 in EDX indicates if it's HT capable */
> +       if (!(edx & 0x10000000))
> +               return false;
> +
> +       total_logical_processors = (ebx >> 16) & 0xff;
> +
> +       ecx = 0;
> +       cpuid(4, &eax, &ebx, &ecx, &edx);
> +       total_cores = ((eax >> 26) & 0x3f) + 1;
> +
> +       /* Thread nums per core */
> +       return (total_logical_processors / total_cores) > 1;
> +}
> +

This function can be simplified as below,

static bool ht_enabled()
{
        if (!cpu_has(&boot_cpu_data, X86_FEATURE_HT))
                return false;

        return smp_num_siblings > 1;
}

But this still can't detect if HT is on or off.
smp_num_siblings is always 2 even if HT is disabled in BIOS.

Any idea how to detect if HT is on or not?

Thanks,
Lin Ming

>  static int intel_pmu_cpu_prepare(int cpu)
>  {
>        struct cpu_hw_events *cpuc = &per_cpu(cpu_hw_events, cpu);
> +
> +       if (!ht_enabled(cpu))
> +               return NOTIFY_OK;
> 
>        cpuc->per_core = kzalloc_node(sizeof(struct intel_percore),
>                                      GFP_KERNEL, cpu_to_node(cpu));
> @@ -1073,6 +1102,15 @@ static void intel_pmu_cpu_starting(int cpu)
>        int core_id = topology_core_id(cpu);
>        int i;
> 
> +       init_debug_store_on_cpu(cpu);
> +       /*
> +        * Deal with CPUs that don't clear their LBRs on power-up.
> +        */
> +       intel_pmu_lbr_reset();
> +
> +       if (!ht_enabled(cpu))
> +               return;
> +
>        for_each_online_cpu(i) {
>                struct intel_percore *pc = per_cpu(cpu_hw_events, i).per_core;
> 
> @@ -1085,12 +1123,6 @@ static void intel_pmu_cpu_starting(int cpu)
> 
>        cpuc->per_core->core_id = core_id;
>        cpuc->per_core->refcnt++;
> -
> -       init_debug_store_on_cpu(cpu);
> -       /*
> -        * Deal with CPUs that don't clear their LBRs on power-up.
> -        */
> -       intel_pmu_lbr_reset();
>  }
> 
>  static void intel_pmu_cpu_dying(int cpu)
> --
> 1.7.3
> 
> 
> 
> 
> 
> --
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