From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AFB4533711D; Fri, 17 Oct 2025 15:01:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760713294; cv=none; b=bMxFfADfJ6hEQ/FzZ/mtnuecw6lidKQ04RK8gn8CztjjuRdBDaTF5sJdvtimxi++XeAKuCgpeDDcT6bPzrwdEKeJNItq5p6hkqZjZSsRlhUjWXoc7KRjLe/WDqyoGEeqRi1HiJPzieTMnr+fS2p5UChWMpsDSy2m1qidlaKuiuA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760713294; c=relaxed/simple; bh=aVEBdYs0yBYpk4F32BB2Cp2eEoFiHHIVi+K1xfhsNC4=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=ly+dtWJclteeqPA3ncVN97vjAONwMOOL9CbDIr1mtsqFFcHocB7lLY61aRAzjg4Hjr1nmasQCwk3RLyVoOrfvRddoo1JIkqvSpVhUaU2jJMhU5+bp2tRgCZeQXUjuDbVE2LLTdnj0Qy5HjAdT2rFB0uu8X2szxvb2HHS+zRpC/8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=dDZC6Ki9; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="dDZC6Ki9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 05109C4CEE7; Fri, 17 Oct 2025 15:01:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760713294; bh=aVEBdYs0yBYpk4F32BB2Cp2eEoFiHHIVi+K1xfhsNC4=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=dDZC6Ki9rOSpqid7v/VEzHihGvvL4VDIsT7VpFPX+Eymfzp3wZNf0VjxY7JuR4fSY IAsxIqSILjYuf44DwymkWFMvGB1c+HUeAZn4Cnks57ajdE+k84kPN8NkH6BFnjlFPl enobg0IJqsGt0NfAipRW2xuqapmldWA5kLwumZqXDyf0zkLZ0NmLPqWE8/p2maJWYs PYzblvP5Hjo2cXLbXaLw3rUPkOAJtMmIqVKyH19nDkbFY4rrq8zY7n2BEVpM++SkYB VIZtYK0LgoTnHav21aJ87aDDt5KEVD+y0ynL1bt3UQXUYfNO4cbCtZmw/CNB9/4LiJ XHymPb4NGBqEg== Date: Sat, 18 Oct 2025 00:01:30 +0900 From: Masami Hiramatsu (Google) To: Steven Rostedt Cc: Mark Rutland , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v3 1/2] tracing: Allow tracer to add more than 32 options Message-Id: <20251018000130.aa69bd5b6670715b1c52d387@kernel.org> In-Reply-To: <20251015172020.5966beaf@gandalf.local.home> References: <175918528341.65920.10238038992631012350.stgit@devnote2> <175918529300.65920.15856373929947126262.stgit@devnote2> <20251015172020.5966beaf@gandalf.local.home> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 15 Oct 2025 17:20:20 -0400 Steven Rostedt wrote: > On Tue, 30 Sep 2025 07:34:53 +0900 > "Masami Hiramatsu (Google)" wrote: > > > --- a/kernel/trace/trace.c > > +++ b/kernel/trace/trace.c > > @@ -86,6 +86,11 @@ void __init disable_tracing_selftest(const char *reason) > > #define tracing_selftest_disabled 0 > > #endif > > > > +/* Define TRACE_ITER_* flags. */ > > +#undef C > > +#define C(a, b) const u64 TRACE_ITER_##a = (1ULL << TRACE_ITER_##a##_BIT); > > +TRACE_FLAGS > > + > > > > > #undef C > > -#define C(a, b) TRACE_ITER_##a = (1 << TRACE_ITER_##a##_BIT) > > +#define C(a, b) extern const u64 TRACE_ITER_##a; > > > > -enum trace_iterator_flags { TRACE_FLAGS }; > > +TRACE_FLAGS > > +#undef C > > Why all this work when this could have been simply fixed with a: > > -enum trace_iterator_flags { TRACE_FLAGS }; > +enum64 trace_iterator_flags { TRACE_FLAGS }; > > ? I could not find any other enum64 usage, so I doubt it is available. (Does it depend on compiler?) It seems C23 standard support it... > > Not to mention, using const u64 requires saving these numbers in an address > and referencing them, instead of doing it inlined in text. That is, using > u64 instead of enum64 is both slower and wastes more memory. Yeah, I expected that the compiler could easily optimize correctly, but maybe not? Thank you, > > -- Steve > -- Masami Hiramatsu (Google)