linux-kernel - Re: [PATCH 7/7] perf/x86/intel/P4: Fix smp_num

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Message-ID: <YvoN2DTABnRZiJhf@worktop.programming.kicks-ass.net>
Date:   Mon, 15 Aug 2022 11:11:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Zhang Rui <rui.zhang@...el.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hwmon@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com,
        corbet@....net, fenghua.yu@...el.com, jdelvare@...e.com,
        linux@...ck-us.net, len.brown@...el.com
Subject: Re: [PATCH 7/7] perf/x86/intel/P4: Fix smp_num_siblings usage

On Sat, Aug 13, 2022 at 12:41:44AM +0800, Zhang Rui wrote:
> smp_num_siblings can be larger than 2.

Not on a P4 it can't ;-)

> 
> Any value larger than 1 suggests HT is supported.
> 
> Reviewed-by: Len Brown <len.brown@...el.com>
> Signed-off-by: Zhang Rui <rui.zhang@...el.com>
> ---
>  arch/x86/include/asm/perf_event_p4.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/perf_event_p4.h b/arch/x86/include/asm/perf_event_p4.h
> index 94de1a05aeba..b14e9a20a7c0 100644
> --- a/arch/x86/include/asm/perf_event_p4.h
> +++ b/arch/x86/include/asm/perf_event_p4.h
> @@ -189,7 +189,7 @@ static inline int p4_ht_active(void)
>  static inline int p4_ht_thread(int cpu)
>  {
>  #ifdef CONFIG_SMP
> -	if (smp_num_siblings == 2)
> +	if (smp_num_siblings > 1)
>  		return cpu != cpumask_first(this_cpu_cpumask_var_ptr(cpu_sibling_map));
>  #endif
>  	return 0;

Unless Intel plans to respin an P4 with extra siblings on, I don't think
this qualifies for the word 'fix'.