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 F3B70C433FE for ; Wed, 19 Oct 2022 14:36:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229957AbiJSOgL (ORCPT ); Wed, 19 Oct 2022 10:36:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55370 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229755AbiJSOfr (ORCPT ); Wed, 19 Oct 2022 10:35:47 -0400 Received: from mail-wr1-x430.google.com (mail-wr1-x430.google.com [IPv6:2a00:1450:4864:20::430]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8498010CFBD for ; Wed, 19 Oct 2022 07:19:52 -0700 (PDT) Received: by mail-wr1-x430.google.com with SMTP id v1so128169wrt.11 for ; Wed, 19 Oct 2022 07:19:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=A41cmwk6vsfiz18uL26ZksSgKHfvB8mOhlbn7RWroYI=; b=BUGjpY4dFx+tjDzcbqisTqhazVC3FPj/37XmkDVOCQooeKNHql7fJDqPBnfXWy0KZB pvWPDQWEIrkzAdErpRcUPyVTNdC1inAoh8G6LmWvUyZjtIQjbTZ89YajEDu+YUxze9Kq TyIOLsZzmAp5XCHwbw+U5NkhiG26chITfQM3kErJ9qGIhIaI0y+8lzf59ScSiB8hlNjp mQODSfGqWKj8ai+74pMSY+6k4S9qyHyAIOHphWaSGMpW9I8VlgdbH/IIst3OSpj6f0Bv QQW1L4n9snVB/NmmaBVvgSCiDLbIbYOuVDeG0ugdNefybxadBtjOFK7mufwjHLY1Eig2 h/+w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; 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=A41cmwk6vsfiz18uL26ZksSgKHfvB8mOhlbn7RWroYI=; b=I4xp1ym7cW69+FK9sBtbRG+FIsZBgDXs+ILu0gqv8gXogRhmA+AcZzPPYk4Gki6gzJ 7FGfpC39J0jSqoF8rUAuh4XqlTGrXBP5fiKji4we7r25KknGk8gMk8qwHNQU+7u+MaqG 7hPk8/ULZO2B/Sc+JXZyhqt4cPXNX70XZRLLu3QqPUkLlCcRaR05eaJXOCYlk4mst4IO yRj7d+xInMNKG1FzY+HRWHkLi+hJFGX6vBsl9F7hniJIJndD068ZUjOvxJ/ZyVp+r/w0 meAKBySHoPl4DVk6PbgLXqzHuckxaAPjC9CGreKmuUEt7kebWGJlnd88ucytaMBmfVBJ 68Hg== X-Gm-Message-State: ACrzQf2qS9pdDuYHqAoFYHN9LIrUrhlxaXBKyZMyFum47bk1UBqD80fi 39LwpWeLwqtGydzom2GicoReWmbNMNBxvA== X-Google-Smtp-Source: AMsMyM7MyOY4LhwNZXVFDl1sEPdPr+4X15+CS/5kCISrrzEweb7zSBeI2+n/jVXlk3DmY7QlTFrcfw== X-Received: by 2002:a17:907:6d08:b0:78e:e87:5c06 with SMTP id sa8-20020a1709076d0800b0078e0e875c06mr6683796ejc.511.1666188553676; Wed, 19 Oct 2022 07:09:13 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id c21-20020a17090603d500b00764a76d5888sm8899287eja.27.2022.10.19.07.09.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 19 Oct 2022 07:09:13 -0700 (PDT) From: Uros Bizjak To: linux-kernel@vger.kernel.org Cc: Uros Bizjak , Peter Zijlstra , Josh Poimboeuf , Jason Baron , Steven Rostedt , Ard Biesheuvel Subject: [PATCH] jump_label: use atomic_try_cmpxchg in static_key_slow_inc_cpuslocked Date: Wed, 19 Oct 2022 16:08:50 +0200 Message-Id: <20221019140850.3395-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.37.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Use atomic_try_cmpxchg instead of atomic_cmpxchg (*ptr, old, new) == old in static_key_slow_inc_cpuslocked. 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, atomic_try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails, enabling further code simplifications. No functional change intended. Cc: Peter Zijlstra Cc: Josh Poimboeuf Cc: Jason Baron Cc: Steven Rostedt Cc: Ard Biesheuvel Signed-off-by: Uros Bizjak --- kernel/jump_label.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) diff --git a/kernel/jump_label.c b/kernel/jump_label.c index 714ac4c3b556..4d6c6f5f60db 100644 --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -115,8 +115,6 @@ EXPORT_SYMBOL_GPL(static_key_count); void static_key_slow_inc_cpuslocked(struct static_key *key) { - int v, v1; - STATIC_KEY_CHECK_USE(key); lockdep_assert_cpus_held(); @@ -132,11 +130,9 @@ void static_key_slow_inc_cpuslocked(struct static_key *key) * so it counts as "enabled" in jump_label_update(). Note that * atomic_inc_unless_negative() checks >= 0, so roll our own. */ - for (v = atomic_read(&key->enabled); v > 0; v = v1) { - v1 = atomic_cmpxchg(&key->enabled, v, v + 1); - if (likely(v1 == v)) + for (int v = atomic_read(&key->enabled); v > 0; ) + if (likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1))) return; - } jump_label_lock(); if (atomic_read(&key->enabled) == 0) { -- 2.37.3