From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0AE19CD5BD0 for ; Wed, 27 May 2026 13:31:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 164B26B00BA; Wed, 27 May 2026 09:31:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 13CC16B00BC; Wed, 27 May 2026 09:31:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 079816B00BD; Wed, 27 May 2026 09:31:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id F00D86B00BA for ; Wed, 27 May 2026 09:31:02 -0400 (EDT) Received: from smtpin07.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id A1BEC161AAC for ; Wed, 27 May 2026 13:31:02 +0000 (UTC) X-FDA: 84813285564.07.F58E96D Received: from mail.ilvokhin.com (mail.ilvokhin.com [178.62.254.231]) by imf17.hostedemail.com (Postfix) with ESMTP id 983AC4001C for ; Wed, 27 May 2026 13:31:00 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=ilvokhin.com header.s=mail header.b=tD9Y95jH; spf=pass (imf17.hostedemail.com: domain of d@ilvokhin.com designates 178.62.254.231 as permitted sender) smtp.mailfrom=d@ilvokhin.com; dmarc=pass (policy=reject) header.from=ilvokhin.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1779888660; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=kUtPQMqnGRZK4WtBtal4fkwqBGL1onBAC0FZaenXB+Y=; b=wO0r5ZLDkWkSbcTHfI0EEFQT8ogZhRJyNsIoMOSvx6SxDE5hqj//RaVLE7Qpljl20gvjq7 OTtB49Eei0iaLZGTZwQKFPQNOgVIZGmW0soRHILTIEndfk1YRyt+HakPS/taEHmzVh19EK lvh5Ay/LUooZSKrGmmtMyjy8q/0bWfM= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=ilvokhin.com header.s=mail header.b=tD9Y95jH; spf=pass (imf17.hostedemail.com: domain of d@ilvokhin.com designates 178.62.254.231 as permitted sender) smtp.mailfrom=d@ilvokhin.com; dmarc=pass (policy=reject) header.from=ilvokhin.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1779888660; a=rsa-sha256; cv=none; b=4Fo0fg9qi/FXMK8AZ1g4t5B26YFpaLni7nKRZc2OMzuU3Ti0iyE2KkoSpimn9VdN74k/z0 fG9aIlk6gmKUZr6CQ5lwSEh0pK0dWUvOEqPJNqbKRhiPVdi7iXvNh16CNb1FoGLzl6uTdo se5exOd67PoEAvy0bvE0QMIh7aSD//w= Received: from shell.ilvokhin.com (shell.ilvokhin.com [138.68.190.75]) (Authenticated sender: d@ilvokhin.com) by mail.ilvokhin.com (Postfix) with ESMTPSA id A4CA2D0D06; Wed, 27 May 2026 13:30:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ilvokhin.com; s=mail; t=1779888658; bh=kUtPQMqnGRZK4WtBtal4fkwqBGL1onBAC0FZaenXB+Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=tD9Y95jHJ7FHOR/3K3r+mZ2uCwLkbP7wrlCEb9kG3J6t+6n9iKA3+dtPEa4P98bh/ o5ovibdCKYI+Qo2jmZQ0eu+Zv4aRy24lOcvlMPgLYo/rPTGo6fKNw9U9ZrOf+VboDg XtEX60Utm7kiii60sP4mieyLYPGASkfm5fIew4eo= Date: Wed, 27 May 2026 13:30:57 +0000 From: Dmitry Ilvokhin To: Peter Zijlstra Cc: Ingo Molnar , Will Deacon , Boqun Feng , Waiman Long , Thomas Bogendoerfer , Juergen Gross , Ajay Kaher , Alexey Makhalov , Broadcom internal kernel review list , Thomas Gleixner , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Arnd Bergmann , Dennis Zhou , Tejun Heo , Christoph Lameter , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org, virtualization@lists.linux.dev, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, kernel-team@meta.com, "Paul E. McKenney" Subject: Re: [PATCH v6 5/7] locking: Add contended_release tracepoint to qspinlock Message-ID: References: <5d7ea75ffe74a785e6b234ada9f23c6373d4b4c1.1777999826.git.d@ilvokhin.com> <20260513193342.GB2545104@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 5pbedo5rjeswfkdrfe9bjs3eg4o6kn1o X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 983AC4001C X-HE-Tag: 1779888660-64837 X-HE-Meta: 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 F+F3U0Zy khvWIIM7bJk2ZSixvQ+JsMCMCpEGQ76Dg5GmFinoBhrEwXpDAS0R4Z2qC6wCHhhcsLPdTPEJTZPcQBNXnvtcwcO9MtqA5chIRSEoDAch9vrMc6/Oaetl1mwH9muEEHG92cpx1LixGDpvzc1F2zYxq3MB3URIDneaX2N2tvQBCRdBFTXzo+OB1XV0DqS7wg1lKkLRoT8LpEF5rId1wM/VuOMmkMpmVjxUH4dyjuxOyg2BXfD8XJyw9MBXzfyYGcCXleB4PT9gYBfS5bZLojLSuCJabehDSZuyoFQ7b Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Peter, Gentle ping on this. I wanted to check if the assembly analysis in my previous reply changed the picture at all. You were right that the commit message was misleading about the total size increase: it's 9 bytes per call site, not just the NOP. That said, when I looked at the executed path with the tracepoint disabled, the only addition is the 2-byte NOP (xchg %ax,%ax). Both the baseline and instrumented _raw_spin_unlock() fit within a single 64-byte cache line, and I wasn't able to measure any difference with locktorture: lock() cost completely dominates, unlock() accounts for less than 1% of the total, so any overhead is indistinguishable from noise. If the cost is still a concern, I see two possible paths forward: 1. Guard the spinlock/qrwlock instrumentation behind a Kconfig option (disabled by default), so only kernels that explicitly opt in pay the cost. 2. Drop the spinlock/qrwlock instrumentation entirely and keep contended_release for sleepable locks only. Happy to go whichever direction you prefer.