From nobody Tue Feb 10 06:06:07 2026 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 9368F27F4CA; Mon, 29 Dec 2025 19:11:07 +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=1767035467; cv=none; b=Enhf8i/KazqImsL/mV7ma0QP/wk65lEhrgdxK7zvwiO+wXIQ3R1YQrT+yX0axK+u8WqWtkNR7m5gxAF/FJ04Gao6KTP4EEXpKWORPX2G4SkKUq8M/Uc05DdV0s6F6/ViAGCs+wAQj56MWX0A7AH1s0+vULau4De0PaED0FOuXIM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767035467; c=relaxed/simple; bh=Ax7FBvNwaT/XyPQJp8bumqr3pkAZvIxwCUWKEB+5I40=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=pd6Hv6kHT9+HnPI5oAg3X9BDdNBvLHZgiRXOzemEcp3p0oeFgXnKRlReFb7DD6bxA6qADmht3m7Pn0XKH2EdyxtzZd6CQIj29adfBjAx7dQcc2r6eQ2phbjAstaYCbRRx+J+tA5PM/D4yso07zbCUY/ipyA6CW6jL8hrb1HibTo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kBtkOgI7; 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="kBtkOgI7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F65EC2BC87; Mon, 29 Dec 2025 19:11:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767035467; bh=Ax7FBvNwaT/XyPQJp8bumqr3pkAZvIxwCUWKEB+5I40=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kBtkOgI7FntPLyVBT9mVPpSLqozf4X28y1qnhCHDQWIy4bcYWvqujwWFRqcU29j4V F93hqWB5o/+Yg0qLpVwjdTZGTuLyRbYHBBOWlu7dhExKrj9yhSNZv36K6lVNGTRwfp QeFNldkeTSacIPbBJZ972g88LKSYkaZMTGHFx7iTPqRyiPNE7U4Yud6jNtxROzt9P4 yABjw3hbMSAwS4QhPWzbEEVBcKUOK9WX1wGVaDeSJq6ezABE5w5yT9qqgXigW2Rawm V/1Q9Jj4OLSwi7sb/PBPzNsdtQvThcxnWzDfEW+ufDIqJ74qlwgqIXnfDX8cpHpZF4 UeFcJk8NU9Wgw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 77A79CE10F4; Mon, 29 Dec 2025 11:11:06 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" , Andrii Nakryiko , Alexei Starovoitov , Peter Zijlstra , bpf@vger.kernel.org Subject: [PATCH v4 6/9] rcu: Update Requirements.rst for RCU Tasks Trace Date: Mon, 29 Dec 2025 11:11:01 -0800 Message-Id: <20251229191104.693447-6-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This commit updates the documentation to declare that RCU Tasks Trace is implemented as a thin wrapper around SRCU-fast. Signed-off-by: Paul E. McKenney Cc: Andrii Nakryiko Cc: Alexei Starovoitov Cc: Peter Zijlstra Cc: --- .../RCU/Design/Requirements/Requirements.rst | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/Documentation/RCU/Design/Requirements/Requirements.rst b/Docum= entation/RCU/Design/Requirements/Requirements.rst index ba417a08b93df..b5cdbba3ec2e7 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -2780,12 +2780,12 @@ Tasks Trace RCU ~~~~~~~~~~~~~~~ =20 Some forms of tracing need to sleep in readers, but cannot tolerate -SRCU's read-side overhead, which includes a full memory barrier in both -srcu_read_lock() and srcu_read_unlock(). This need is handled by a -Tasks Trace RCU that uses scheduler locking and IPIs to synchronize with -readers. Real-time systems that cannot tolerate IPIs may build their -kernels with ``CONFIG_TASKS_TRACE_RCU_READ_MB=3Dy``, which avoids the IPIs= at -the expense of adding full memory barriers to the read-side primitives. +SRCU's read-side overhead, which includes a full memory barrier in +both srcu_read_lock() and srcu_read_unlock(). This need is handled by +a Tasks Trace RCU API implemented as thin wrappers around SRCU-fast, +which avoids the read-side memory barriers, at least for architectures +that apply noinstr to kernel entry/exit code (or that build with +``CONFIG_TASKS_TRACE_RCU_NO_MB=3Dy``. =20 The tasks-trace-RCU API is also reasonably compact, consisting of rcu_read_lock_trace(), rcu_read_unlock_trace(), --=20 2.40.1