From nobody Wed Oct 1 22:32:39 2025 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 D5849303A22; Wed, 1 Oct 2025 14:48:39 +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=1759330119; cv=none; b=L8DRqrXcZl3iLSgbf+6qnf5KnS+LWT/lgTa8iB94dekx+esV7ADOD/G/Wj6x6FEeYLwUAJAfJIWuRaCTbvh512gh/ZUpcOlCOeZhoDWrsvIxjUXcoKppSdFmfpdFADD02HxXweFA90GeGWslXOVtorR6vq07GZ2imnv9vuAQe1k= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759330119; c=relaxed/simple; bh=1LD05Jje7JY4+QRieuy7/gMogSMrNyvAzrT45QnCY+Y=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=ZNj9sR1Z4d7xQZ3CXzTsL0GqLeISETsOKavRBgUNqNhcn0lLVNaq4yxt6ZtiMd5VM9ueV7pwmLh8AsTgfyZuB9MvASTNq4Hdg5NKJhzn9YVfirJ6OlzRRHVMDgpq6B/dPvOtWsdXBGc8yC/Ss1mNFps4mfhGVMcYGwuZUKJ7pgQ= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fGwYKN9Q; 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="fGwYKN9Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5E97BC4CEF9; Wed, 1 Oct 2025 14:48:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1759330119; bh=1LD05Jje7JY4+QRieuy7/gMogSMrNyvAzrT45QnCY+Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fGwYKN9Q2GnrQ2++a4QBcrC3JPlemY5oGyYqbWqaBzOHRdf872rSKrTknDuOrFqFU GdmkAG9gc4Wa7ziRv40WAdYo1fuFXLWHlXgcW6AOTeqroznLCqh6pg+K/GYgAfM+pt aTM9mm7TJZ2t8SmUSx+4L1XRs2JfEIIwRFHwHi4pPw4If76NvCtiIf9WlSAVymvRtZ 9lKLptiLH0IeLPO6MZ9uhZhTMLk42z04sWlAu093AjCMO3GsnaJkQTDfIkLNUgBHU1 966/Z4x4yC2aLM2aubQKW0gHam6dClRefZ3nAlxeqa2oXGWp3DBiqyGpgNRe5RburP J6gNWXMb3+MOw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 77EBBCE12C3; Wed, 1 Oct 2025 07:48:34 -0700 (PDT) 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 v2 09/21] rcu: Update Requirements.rst for RCU Tasks Trace Date: Wed, 1 Oct 2025 07:48:20 -0700 Message-Id: <20251001144832.631770-9-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <7fa58961-2dce-4e08-8174-1d1cc592210f@paulmck-laptop> References: <7fa58961-2dce-4e08-8174-1d1cc592210f@paulmck-laptop> 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 f24b3c0b9b0dc6..4a116d7a564edc 100644 --- a/Documentation/RCU/Design/Requirements/Requirements.rst +++ b/Documentation/RCU/Design/Requirements/Requirements.rst @@ -2779,12 +2779,12 @@ 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