linux-kernel - Re: [PATCH] perf/x86/intel: Use early_initcall() to hook bts

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Message-ID: <820b6d4f-b4b1-43fb-9829-5ff617eca5f9@linux.intel.com>
Date: Thu, 19 Jun 2025 09:10:34 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
 Adrian Hunter <adrian.hunter@...el.com>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Kan Liang <kan.liang@...ux.intel.com>, Andi Kleen <ak@...ux.intel.com>,
 Eranian Stephane <eranian@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 Andrew Zaborowski <andrew.zaborowski@...el.com>,
 Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [PATCH] perf/x86/intel: Use early_initcall() to hook bts_init()

Kindly ping...   Thanks.

On 6/6/2025 7:16 PM, Dapeng Mi wrote:
> After the commit 'd971342d38bf ("perf/x86/intel: Decouple BTS
>  initialization from PEBS initialization")' is introduced, x86_pmu.bts
> would initialized in bts_init() which is hooked by arch_initcall().
>
> Whereas init_hw_perf_events() is hooked by early_initcall(). Once the
> core PMU is initialized, nmi watchdog initialization is called
> immediately before bts_init() is called. It leads to the BTS buffer is
> not really initialized since bts_init() is not called and x86_pmu.bts is
> still false at that time. Worse, BTS buffer would never be initialized
> then unless all core PMU events are freed and reserve_ds_buffers()
> is called again.
>
> Thus aligning with init_hw_perf_events(), use early_initcall() to hook
> bts_init() to ensure x86_pmu.bts is initialized before nmi watchdog
> initialization.
>
> Fixes: d971342d38bf ("perf/x86/intel: Decouple BTS initialization from PEBS initialization")
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  arch/x86/events/intel/bts.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
> index 9560f693fac0..f0d9729ed255 100644
> --- a/arch/x86/events/intel/bts.c
> +++ b/arch/x86/events/intel/bts.c
> @@ -642,4 +642,4 @@ static __init int bts_init(void)
>  
>  	return perf_pmu_register(&bts_pmu, "intel_bts", -1);
>  }
> -arch_initcall(bts_init);
> +early_initcall(bts_init);
>
> base-commit: e7d952cc39fca34386ec9f15f68cb2eaac01b5ae