From nobody Fri Oct 3 00:00:56 2025 Received: from mail-wm1-f54.google.com (mail-wm1-f54.google.com [209.85.128.54]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 076272D130C for ; Tue, 9 Sep 2025 09:26:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.54 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757409981; cv=none; b=skk8swTCMXuMVXW7kw5uw7XcuY3tPbWQlRGi4qoajknz/LypoqEUD8olTxPONZAuGmKcxo70U/P9yA7aIN9QCS7vddRNNdZ7LMVcZNex2vUI9YkjSSRdrdgddhh8+sGanHyH9+UJCYpOYNl+RyY9do8bCpGGzoxeuQba9/X/Ba4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757409981; c=relaxed/simple; bh=hIv0M1xI8frJxsikJ5DnOhEUO2kleaKFfsP8HrIZwSw=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=PF8GPYjwV3m22m/OqSjR/Ecom2bFDYqPuYSdi11ZoBj325EgVDPTaDmTrLwloAiUh/IDzNxl3Nn3HVtxcQEeCB598hPIRyg8g4rE18eCk1D/GGJ1ff3XH4ENAGAi+Y9LD108QlD0A9pgj5APmncQtHTxYWP9DLfq5XVzvi5OrrI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=F1kUUruk; arc=none smtp.client-ip=209.85.128.54 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="F1kUUruk" Received: by mail-wm1-f54.google.com with SMTP id 5b1f17b1804b1-45ddddbe31fso18266385e9.1 for ; Tue, 09 Sep 2025 02:26:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1757409978; x=1758014778; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=4ZBpNNflTkMWuUHCsBPf2naE+qYZiwrT7qmaFKr9fdw=; b=F1kUUruklAMZIxcZr51n7oEC3UR5qZsVyCCqIbGXjeIkWQbcB6UO61SYsYELXUw9TA A+1FwJ1R/XJ/XszBYZ9Vl6DpCHWTwhFMwagIB4fWsyPtlDYfXbxxe1eFOa2Htx1EdvTI vqxvtMBz8c422Y+KjI74INowrdf+fXKP7ksRqVBBSgl0EG0Vty+7Iq3yrW4HsAHI36LG PVa1w729ZkQxh14qtbQ3WKl31+OYpNVXivwIoWNkqCITPUT4anO94o4nVf/SpMFa++SD vwMGCGFBG1CNYrRDnTa4JgksNQ11QNIZZ9mQVL3FTzTqSVmFYuA+Ad5PM6Lo9CgBgBru 9Idw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757409978; x=1758014778; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=4ZBpNNflTkMWuUHCsBPf2naE+qYZiwrT7qmaFKr9fdw=; b=ejz1b6w9+UPiz64eybtZAsqFdVUcJGOF18XcGrdGxj2uQQjN1pTOKarrcla17W+mvK 3aetHWsqg5kBntUIs2Up19DQqZYag6nGMKOGygwWqQj7RMcuSs8ScmZag1T/PdlwVFLM KFhS9Y3HpnTeXQAroGkE1mnLAQj4vHpG8IfRbat29zgYlamjANt5lIn3vxnXMoC5JxbQ OPVOgj8PBB2VSfV6ZaT9jPONrjjcsunfAMT01BW45eX08RlOYE6EVnAs+W03fJeMR6Ur 3EvEQefU+JaJTvPIO6tB/YL9ysbBuC0i/eES9Hwqv4DfyKo0lwkYGuKxMDsUAxeKQyoS es6g== X-Gm-Message-State: AOJu0YxVMFlWGuDUFagYRk9FlQpOykFqqydShS7pe4cEhpKbMW6sKh3o 4z8Eru1ZwqaWwsJInwZu4lQCBE2Q6YhCN4X5mnK1lQYHv3NUkvhgF3V6croivQ== X-Gm-Gg: ASbGncsjtEk9SHcfbwb6JtigX/V4a/z3cfqeNc8+AyDPNOkaX+YHZ3CUpoVP/Z7zhQ9 mGjPxF6T0+02D9b5FGiQsucuEqz2X2sdoR6zM5qAXt8q0Eu+s/7h3emECNlmQ6j2ohv6RyyPbxO S7KAb5OQ89vm3JgVZBqeeiysbycZd3JPwGRTSYjlMpO2iLxslJj62dziY8CemEI4hz2RDrTSl/P Z1VjAHz1b9rLEOQFeAhwKk3BmTRhyYuJe11p6pIWlZld+j0v3cWSwI/Ipi+uqO3K8Goc8MfTRqk bGvdotvfQFVXRjKq7fndlN9ubXQKyJ5J119vNrgHasBvJdrvMRddlmgD///3U8zep2drs3rmOi+ +sWWrdDzimCF87ml+IMm5/TI= X-Google-Smtp-Source: AGHT+IGWrx1bb2cUBMB5LIaILRjDOZfhZW+ZgLyibZtX8apgT8z/wC4Ly25gHnGwXQHSNQFe0S7lZA== X-Received: by 2002:a05:600c:4fcd:b0:456:43c:dcdc with SMTP id 5b1f17b1804b1-45dddee3ae6mr106910395e9.33.1757409977589; Tue, 09 Sep 2025 02:26:17 -0700 (PDT) Received: from fedora ([193.77.86.199]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-45dd4affb6bsm196955685e9.1.2025.09.09.02.26.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Sep 2025 02:26:17 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider Subject: [PATCH RESEND -tip] sched/core: use try_cmpxchg() in mm_cid_pcpu_unset() Date: Tue, 9 Sep 2025 11:25:52 +0200 Message-ID: <20250909092606.1678763-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.51.0 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" Use try_cmpxchg() instead of cmpxchg (*ptr, old, new) =3D=3D old in mm_cid_pcpu_unset(). x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg. Also, try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling substantial source code simplifications. The generated asm code improves from: d6cd: eb 18 jmp d6e7 <...> d6cf: 65 48 8b 0d 00 00 00 mov %gs:0x0(%rip),%rcx d6d6: 00 d6d7: 89 d0 mov %edx,%eax d6d9: 4c 01 c1 add %r8,%rcx d6dc: f0 0f b1 71 08 lock cmpxchg %esi,0x8(%rcx) d6e1: 39 c2 cmp %eax,%edx d6e3: 74 3a je d71f <...> d6e5: 89 c2 mov %eax,%edx d6e7: 83 fa ff cmp $0xffffffff,%edx d6ea: 75 e3 jne d6cf <...> d6ec: 48 c7 83 20 0a 00 00 movq $0xffffffffffffffff,0xa20(%rbx) d6f3: ff ff ff ff ... d71f: 81 e2 ff ff ff 7f and $0x7fffffff,%edx d725: f0 48 0f b3 95 90 05 lock btr %rdx,0x590(%rbp) d72c: 00 00 d72e: eb bc jmp d6ec <...> to a substatially more streamlined: d6cd: 83 f9 ff cmp $0xffffffff,%ecx d6d0: 74 23 je d6f5 <...> d6d2: 65 48 8b 15 00 00 00 mov %gs:0x0(%rip),%rdx d6d9: 00 d6da: 89 c8 mov %ecx,%eax d6dc: 4c 01 c2 add %r8,%rdx d6df: f0 0f b1 72 08 lock cmpxchg %esi,0x8(%rdx) d6e4: 75 42 jne d728 <...> d6e6: 81 e1 ff ff ff 7f and $0x7fffffff,%ecx d6ec: f0 48 0f b3 8d 90 05 lock btr %rcx,0x590(%rbp) d6f3: 00 00 d6f5: 48 c7 83 20 0a 00 00 movq $0xffffffffffffffff,0xa20(%rbx) d6fc: ff ff ff ff ... d728: 89 c1 mov %eax,%ecx d72a: eb a1 jmp d6cd <...> No functional change intended. Signed-off-by: Uros Bizjak Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: Valentin Schneider --- kernel/sched/sched.h | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index b5367c514c14..d7f2cf458aa5 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -3557,21 +3557,16 @@ static inline void mm_cid_put_lazy(struct task_stru= ct *t) static inline int mm_cid_pcpu_unset(struct mm_struct *mm) { struct mm_cid __percpu *pcpu_cid =3D mm->pcpu_cid; - int cid, res; + int cid; =20 lockdep_assert_irqs_disabled(); cid =3D __this_cpu_read(pcpu_cid->cid); - for (;;) { + do { if (mm_cid_is_unset(cid)) return MM_CID_UNSET; - /* - * Attempt transition from valid or lazy-put to unset. - */ - res =3D cmpxchg(&this_cpu_ptr(pcpu_cid)->cid, cid, MM_CID_UNSET); - if (res =3D=3D cid) - break; - cid =3D res; - } + /* Attempt transition from valid or lazy-put to unset. */ + } while (!try_cmpxchg(&this_cpu_ptr(pcpu_cid)->cid, &cid, MM_CID_UNSET)); + return cid; } =20 --=20 2.51.0