From: Peter Zijlstra <peterz@infradead.org>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Ingo Molnar <mingo@kernel.org>, Uros Bizjak <ubizjak@gmail.com>
Subject: Re: [PATCH v2] noinstr: Use asm_inline() in instrumentation_{begin,end}()
Date: Tue, 15 Apr 2025 09:48:49 +0200 [thread overview]
Message-ID: <20250415074849.GJ5600@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <165d2a0b882050f3f6cc0315af66cd2d16e5925b.1744676674.git.jpoimboe@kernel.org>
On Mon, Apr 14, 2025 at 05:27:11PM -0700, Josh Poimboeuf wrote:
> Use asm_inline() in the instrumentation begin/end macros to prevent the
> compiler from making poor inlining decisions based on the length of the
> objtool annotations.
>
> Without the objtool annotations, each macro resolves to a single NOP.
> Using inline_asm() seems obviously correct here as it accurately
> communicates the actual code size to the compiler.
>
> These macros are used by WARN() and lockdep, so this change can affect a
> lot of functions.
>
> For a defconfig kernel built with GCC 14.2.1, bloat-o-meter reports a
> 0.17% increase in text size:
>
> add/remove: 74/352 grow/shrink: 914/353 up/down: 80747/-47120 (33627)
> Total: Before=19460272, After=19493899, chg +0.17%
Hmm, I was surprised that defconfig was affected at all. Why does
defconfig have DEBUG_ENTRY on?
next prev parent reply other threads:[~2025-04-15 7:48 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-04-15 0:27 Josh Poimboeuf
2025-04-15 7:48 ` Peter Zijlstra [this message]
2025-04-15 14:52 ` Josh Poimboeuf
2025-04-22 12:02 ` Ingo Molnar
2025-04-22 13:22 ` Uros Bizjak
2025-04-22 20:05 ` Ingo Molnar
2025-04-23 7:07 ` Uros Bizjak
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