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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 95C95C83F27 for ; Wed, 30 Aug 2023 19:03:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241445AbjH3TCZ (ORCPT ); Wed, 30 Aug 2023 15:02:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55966 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S245476AbjH3PQj (ORCPT ); Wed, 30 Aug 2023 11:16:39 -0400 Received: from mail-ed1-x52f.google.com (mail-ed1-x52f.google.com [IPv6:2a00:1450:4864:20::52f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B14CC1A2 for ; Wed, 30 Aug 2023 08:16:36 -0700 (PDT) Received: by mail-ed1-x52f.google.com with SMTP id 4fb4d7f45d1cf-52a0856b4fdso7417385a12.1 for ; Wed, 30 Aug 2023 08:16:36 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20221208; t=1693408595; x=1694013395; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=oW9pYlM91CH6rczFdRvlNOM5/TsYTpBNFeuKY78V0hk=; b=r0I37HUilkc7Nf/SKu6oJflZOsQ4GvS8H/0iptua3hTYveL7+DNv5YO8oO/L6tlsdt jG0IRkKAsEXNN74Otsu4vRnCCtnQ6AMTqSTLlizvVJbiM55ZfOCX7l7H5DsPofj9XX9e kD4mThtaMTZ/ALsYMQJZ1R/2T2cOX+QO/ggb4qWSfQ4lqtLCI7To82OVhwtPpUfMqyXE oudCfleYd+ZrzvBZq9BPIT4d1Z2MLH8fmnjdHVIfnOq78XiJsQrfFLyIK/uQskxlJ4q6 qvQZe9blr1kUx/tfwN+sziNQv0AxQOmobJtMsU/BeVIBhLRVmIQPWCAed93/CihPOVhA 4nQw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1693408595; x=1694013395; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=oW9pYlM91CH6rczFdRvlNOM5/TsYTpBNFeuKY78V0hk=; b=DlHL1/cAjhV/LrmTt44cqmHuCF92IdOPjn9taJjGP2ZCyQfX5gTuB7kGyhQzoCWwTo CxrqaLb3FLy6qaYuisel+zFfCWXsqszp8Fty/kXohcqOP4EBJl8gn0cAqhZ6VnFo4/hP LrvudTo9jb8WCzi5G8sLzH08Y8beXAOGhZfg+ziaSu9U7r4DwjaVLtA5tsK8LhQqTO1L DIKw/YB7jIQSKV2OsN1Y4GpGDUQvv2TUqT7zR8GgvaLpbU2ZF3lpjVeaa6y1dKNRD/cI VCy2qhKAQOb/2qGtNcpqp6XpprzUfD0Jw/l99a6mNIEjKeK/rMDlLTsfso2/7IdKLnpg /9HA== X-Gm-Message-State: AOJu0YyMD/lYVfS/fe7mERT4PmZVswuP8F9x36StP3WefHSYghOZTmkv amp592aw0tqB1SWwQ58qYM4= X-Google-Smtp-Source: AGHT+IGg7yKpRNsAQ8mT/HutPWO9Avy1WCmNhDFXrnEXV1fYHNqEg/krALLP5jXb1Kv+R2C4TH9m0g== X-Received: by 2002:a17:907:7898:b0:9a2:139:f469 with SMTP id ku24-20020a170907789800b009a20139f469mr1938735ejc.69.1693408595175; Wed, 30 Aug 2023 08:16:35 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id k11-20020a1709063e0b00b009a1a653770bsm7241627eji.87.2023.08.30.08.16.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Aug 2023 08:16:34 -0700 (PDT) From: Uros Bizjak To: x86@kernel.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" Subject: [PATCH 2/2] x86/percpu: Use raw_cpu_try_cmpxchg in preempt_count_set Date: Wed, 30 Aug 2023 17:13:57 +0200 Message-ID: <20230830151623.3900-2-ubizjak@gmail.com> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230830151623.3900-1-ubizjak@gmail.com> References: <20230830151623.3900-1-ubizjak@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use raw_cpu_try_cmpxchg instead of raw_cpu_cmpxchg (*ptr, old, new) == old. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after cmpxchg (and related move instruction in front of cmpxchg). Also, raw_cpu_try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. No functional change intended. Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: Dave Hansen Cc: "H. Peter Anvin" Signed-off-by: Uros Bizjak --- arch/x86/include/asm/preempt.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index 2d13f25b1bd8..4527e1430c6d 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -31,11 +31,11 @@ static __always_inline void preempt_count_set(int pc) { int old, new; + old = raw_cpu_read_4(pcpu_hot.preempt_count); do { - old = raw_cpu_read_4(pcpu_hot.preempt_count); new = (old & PREEMPT_NEED_RESCHED) | (pc & ~PREEMPT_NEED_RESCHED); - } while (raw_cpu_cmpxchg_4(pcpu_hot.preempt_count, old, new) != old); + } while (!raw_cpu_try_cmpxchg_4(pcpu_hot.preempt_count, &old, new)); } /* -- 2.41.0