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From: Chen Pei <cp0613@linux.alibaba.com>
To: David Laight <david.laight.linux@gmail.com>
Cc: acme@kernel.org, peterz@infradead.org, mingo@redhat.com,
	namhyung@kernel.org, mark.rutland@arm.com,
	alexander.shishkin@linux.intel.com, jolsa@kernel.org,
	irogers@google.com, adrian.hunter@intel.com,
	james.clark@linaro.org, leo.yan@linux.dev,
	john.g.garry@oracle.com, will@kernel.org, mike.leach@arm.com,
	pjw@kernel.org, palmer@dabbelt.com, guoren@kernel.org,
	linux-perf-users@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] perf tsc: Replace the compile-time TSC support check with a weak hook
Date: Tue, 29 Sep 2026 17:08:13 +0800	[thread overview]
Message-ID: <20260929090818.2651-1-cp0613@linux.alibaba.com> (raw)
In-Reply-To: <20260929092850.697bce16@pumpkin>

Hi David,

Thanks a lot for the review.

> If you mark the prototype in the .h file "weak" you don't need a default
> - instead check the symbol for being NULL.
>
> Then you can do:
> 	if (!rdtsc)  {
> 		pr_debug("Test not supported on this architecture\n");
> 		return TEST_SKIP;
> 	}

I've just sent v2, which declares the support from the build system
instead, following the existing PERF_HAVE_JITDUMP pattern, so the
decision is made at compile time and there is no symbol left to test for
NULL.

Keeping the __weak rdtsc() stub also means the callers that already call
it unconditionally don't have to grow a NULL check.

Thanks again for the suggestion.

Best regards,
Pei

WARNING: multiple messages have this Message-ID (diff)
From: Chen Pei <cp0613@linux.alibaba.com>
To: David Laight <david.laight.linux@gmail.com>
Cc: acme@kernel.org, peterz@infradead.org, mingo@redhat.com,
	namhyung@kernel.org, mark.rutland@arm.com,
	alexander.shishkin@linux.intel.com, jolsa@kernel.org,
	irogers@google.com, adrian.hunter@intel.com,
	james.clark@linaro.org, leo.yan@linux.dev,
	john.g.garry@oracle.com, will@kernel.org, mike.leach@arm.com,
	pjw@kernel.org, palmer@dabbelt.com, guoren@kernel.org,
	linux-perf-users@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] perf tsc: Replace the compile-time TSC support check with a weak hook
Date: Tue, 29 Sep 2026 17:08:13 +0800	[thread overview]
Message-ID: <20260929090818.2651-1-cp0613@linux.alibaba.com> (raw)
In-Reply-To: <20260929092850.697bce16@pumpkin>

Hi David,

Thanks a lot for the review.

> If you mark the prototype in the .h file "weak" you don't need a default
> - instead check the symbol for being NULL.
>
> Then you can do:
> 	if (!rdtsc)  {
> 		pr_debug("Test not supported on this architecture\n");
> 		return TEST_SKIP;
> 	}

I've just sent v2, which declares the support from the build system
instead, following the existing PERF_HAVE_JITDUMP pattern, so the
decision is made at compile time and there is no symbol left to test for
NULL.

Keeping the __weak rdtsc() stub also means the callers that already call
it unconditionally don't have to grow a NULL check.

Thanks again for the suggestion.

Best regards,
Pei

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

  reply	other threads:[~2026-09-29  9:08 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-09-28  9:47 [PATCH 0/2] perf riscv: Implement rdtsc() Chen Pei
2026-09-28  9:47 ` Chen Pei
2026-09-28  9:47 ` [PATCH 1/2] " Chen Pei
2026-09-28  9:47   ` Chen Pei
2026-09-28  9:54   ` sashiko-bot
2026-09-28 13:42   ` Anup Patel
2026-09-28 13:42     ` Anup Patel
2026-09-28  9:47 ` [PATCH 2/2] perf tsc: Replace the compile-time TSC support check with a weak hook Chen Pei
2026-09-28  9:47   ` Chen Pei
2026-09-28  9:55   ` sashiko-bot
2026-09-28 13:42   ` Anup Patel
2026-09-28 13:42     ` Anup Patel
2026-09-28 16:34   ` Leo Yan
2026-09-28 16:34     ` Leo Yan
2026-09-29  3:40     ` Chen Pei
2026-09-29  3:40       ` Chen Pei
2026-09-29  8:28   ` David Laight
2026-09-29  8:28     ` David Laight
2026-09-29  9:08     ` Chen Pei [this message]
2026-09-29  9:08       ` Chen Pei

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