linux-kernel - Re: [Patch v5 08/19] perf/x86: Enable XMM sampling using sample_simd_vec_reg

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Message-ID: <20251205112516.GU2528459@noisy.programming.kicks-ass.net>
Date: Fri, 5 Dec 2025 12:25:16 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>,
	Eranian Stephane <eranian@...gle.com>,
	Mark Rutland <mark.rutland@....com>, broonie@...nel.org,
	Ravi Bangoria <ravi.bangoria@....com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org, Zide Chen <zide.chen@...el.com>,
	Falcon Thomas <thomas.falcon@...el.com>,
	Dapeng Mi <dapeng1.mi@...el.com>, Xudong Hao <xudong.hao@...el.com>,
	Kan Liang <kan.liang@...ux.intel.com>
Subject: Re: [Patch v5 08/19] perf/x86: Enable XMM sampling using
 sample_simd_vec_reg_* fields

On Wed, Dec 03, 2025 at 02:54:49PM +0800, Dapeng Mi wrote:

> diff --git a/arch/x86/include/uapi/asm/perf_regs.h b/arch/x86/include/uapi/asm/perf_regs.h
> index 7c9d2bb3833b..c3862e5fdd6d 100644
> --- a/arch/x86/include/uapi/asm/perf_regs.h
> +++ b/arch/x86/include/uapi/asm/perf_regs.h
> @@ -55,4 +55,21 @@ enum perf_event_x86_regs {
>  
>  #define PERF_REG_EXTENDED_MASK	(~((1ULL << PERF_REG_X86_XMM0) - 1))
>  
> +enum {
> +	PERF_REG_X86_XMM,
> +	PERF_REG_X86_MAX_SIMD_REGS,
> +};
> +
> +enum {
> +	PERF_X86_SIMD_XMM_REGS      = 16,
> +	PERF_X86_SIMD_VEC_REGS_MAX  = PERF_X86_SIMD_XMM_REGS,
> +};
> +
> +#define PERF_X86_SIMD_VEC_MASK		GENMASK_ULL(PERF_X86_SIMD_VEC_REGS_MAX - 1, 0)
> +
> +enum {
> +	PERF_X86_XMM_QWORDS      = 2,
> +	PERF_X86_SIMD_QWORDS_MAX = PERF_X86_XMM_QWORDS,
> +};
> +
>  #endif /* _ASM_X86_PERF_REGS_H */

I don't understand this bit -- the next few patches add to it for YMM
and ZMM, but what's the point? I don't see why this is needed at all,
let alone why it needs to be UABI.