linux-kernel - Re: [PATCH v2 2/6] perf kvm stat: Remove use of the arch directory

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Message-ID: <20260201170459.GA584@debian-dev>
Date: Mon, 2 Feb 2026 01:04:59 +0800
From: Leo Yan <leo.yan@...ux.dev>
To: Ian Rogers <irogers@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	James Clark <james.clark@...aro.org>,
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
	Mike Leach <mike.leach@...aro.org>, Paul Walmsley <pjw@...nel.org>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Shimin Guo <shimin.guo@...dio.com>, Yunseong Kim <ysk@...lloc.com>,
	Athira Rajeev <atrajeev@...ux.ibm.com>,
	Quan Zhou <zhouquan@...as.ac.cn>,
	Andrew Jones <ajones@...tanamicro.com>,
	Anup Patel <anup@...infault.org>,
	Dapeng Mi <dapeng1.mi@...ux.intel.com>,
	Thomas Falcon <thomas.falcon@...el.com>,
	Blake Jones <blakejones@...gle.com>,
	Swapnil Sapkal <swapnil.sapkal@....com>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Howard Chu <howardchu95@...il.com>,
	Anubhav Shelat <ashelat@...hat.com>,
	Aditya Bodkhe <aditya.b1@...ux.ibm.com>,
	Chun-Tse Shao <ctshao@...gle.com>, Andi Kleen <ak@...ux.intel.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, linux-kernel@...r.kernel.org,
	linux-perf-users@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v2 2/6] perf kvm stat: Remove use of the arch directory

On Sat, Jan 31, 2026 at 12:02:20PM -0800, Ian Rogers wrote:

[...]

> @@ -1666,7 +1661,7 @@ kvm_events_record(struct perf_kvm_stat *kvm, int argc, const char **argv)
>  		return ret;
>  	}
>  
> -	for (events_tp = kvm_events_tp; *events_tp; events_tp++)
> +	for (events_tp = kvm_events_tp(); *events_tp; events_tp++)
>  		events_tp_size++;
>  
>  	rec_argc = ARRAY_SIZE(record_args) + argc + 2 +
> @@ -1681,7 +1676,7 @@ kvm_events_record(struct perf_kvm_stat *kvm, int argc, const char **argv)
>  
>  	for (j = 0; j < events_tp_size; j++) {
>  		rec_argv[i++] = STRDUP_FAIL_EXIT("-e");
> -		rec_argv[i++] = STRDUP_FAIL_EXIT(kvm_events_tp[j]);
> +		rec_argv[i++] = STRDUP_FAIL_EXIT(kvm_events_tp()[j]);
>  	}

Nitpick: we can assign reuse events_tp throughout the
kvm_events_record().  Something like:

  events_tp = kvm_events_tp();
  for (j = 0; events_tp[j]; j++)
       events_tp_size++;

  ...

  for (j = 0; j < events_tp_size; j++) {
       rec_argv[i++] = STRDUP_FAIL_EXIT("-e");
       rec_argv[i++] = STRDUP_FAIL_EXIT(events_tp[j]);
  }

[...]

> +int setup_kvm_events_tp(struct perf_kvm_stat *kvm)
> +{
> +	switch (EM_HOST) {
> +	case EM_PPC:
> +	case EM_PPC64:
> +		return __setup_kvm_events_tp_powerpc(kvm);
> +	default:
> +		return 0;
> +	}
> +}
> +
> +int cpu_isa_init(struct perf_kvm_stat *kvm, const char *cpuid)
> +{
> +	switch (EM_HOST) {
> +	case EM_AARCH64:
> +		return __cpu_isa_init_arm64(kvm);
> +	case EM_LOONGARCH:
> +		return __cpu_isa_init_loongarch(kvm);
> +	case EM_PPC:
> +	case EM_PPC64:
> +		return __cpu_isa_init_powerpc(kvm);
> +	case EM_RISCV:
> +		return __cpu_isa_init_riscv(kvm);
> +	case EM_S390:
> +		return __cpu_isa_init_s390(kvm, cpuid);
> +	case EM_X86_64:
> +	case EM_386:
> +		return __cpu_isa_init_x86(kvm, cpuid);
> +	default:
> +		pr_err("Unsupported kvm-stat host %d\n", EM_HOST);
> +		return -1;
> +	}
> +}

For a general solution, I'd prefer to use "install" + callback methods
rather than the opened code.  E.g., each arch installs a structure
with callbacks:

  struct kvm_stat_arch kvm_stat_aarch64 {
      .setup_events_tp = NULL;
      .cpu_isa_init    = __cpu_isa_init_arm64;
      ...
  };

Then at the init phase, we can install arch's structure:

  switch (EM_HOST) {
  case EM_AARCH64:
      kvm_stat_arch_init(&kvm_stat_aarch64);
      break;
  ...
  }

Afterwards, it is no need to check EM_HOST anymore, it can simply
invoke the arch's callback:

  int cpu_isa_init(struct perf_kvm_stat *kvm, const char *cpuid)
  {
      if (!arch_kvm_stat || !arch_kvm_stat->cpu_isa_init)
          return -1;

      return arch_kvm_stat->cpu_isa_init(kvm, cpuid);
  }

As a result, we can avoid spreading "switch (EM_HOST)" everywhere.

Thanks,
Leo