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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0897BC433FE for ; Thu, 20 Oct 2022 15:36:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-Type: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:References:List-Owner; bh=Xz6rkNFT+N3+z5GHliBzDaeRK81yOrfk7eIGZzmG81Q=; b=sNk9CG8F6V+0lOVc7zGJ2pqCHW eGv3BmZSvgH2zDncb1sme6CjKum4Pc5zh6vMpS8XhEQqB6dy59xD7KKxrhJqZ1CzL60mvcsHLPc4C cEriI278St3zanG6cjrjOqT2HLpROnq0t+P5UTuH3obCsiOqtvXE+8WpkMRi8De7N4XMeqdsR44LJ 23wQsBeVgwGAHEhoB4hkxfoGITXcm7MBfyVx6vga8MaK/AFvxCHzw4dOiDtxphcolkMB75xeMnGXM VwsHi/zWdYTK9dLlygMaJ6f8rLfA9mh0Ij5rr3pEsqUQh9FYv1cFEPXNu3zNmlMaiLrHekHpql4vp MsEzkFhA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1olXaQ-00H7X5-CB; Thu, 20 Oct 2022 15:35:58 +0000 Received: from mail-wm1-x336.google.com ([2a00:1450:4864:20::336]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1olXaN-00H7Us-TG for linux-nvme@lists.infradead.org; Thu, 20 Oct 2022 15:35:57 +0000 Received: by mail-wm1-x336.google.com with SMTP id n16-20020a05600c4f9000b003c17bf8ddecso2695981wmq.0 for ; Thu, 20 Oct 2022 08:35:53 -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=Xz6rkNFT+N3+z5GHliBzDaeRK81yOrfk7eIGZzmG81Q=; b=LrPvFB8gDO64B7UiPcOEb4r4czILVjpCtcxZINcfAFDa3JVnVixw8m/oGT/SX21zP/ Gr0oby3J6kWKup8VmdmabJ/RmMiUTF41qbixfM8VEDJItjOUfbI+i4eL5pPeXKNAC14E dFkAG4sTNCeJGTXP9FerhSiUuerkXXeqxmrzw4EjmqkkUs0TqQd5EofrRaek32k73Lrv hovubnAzUZ9PQje3IfBFZK8uo/EOI95RVgx3leGIGBT81cFNKVXmL2Sc4MI9FZ2Jo2o3 E4+/DFmy8GAK+x+xJAmWJ9xFNcSRq7lHXKBFpaqNZHYOCvETpZaQ5vW86279Aqavyawn TvCw== 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=Xz6rkNFT+N3+z5GHliBzDaeRK81yOrfk7eIGZzmG81Q=; b=uhPMI33NYl0URbx734mIMVrmeh9/FuCAlvDV8Ranxl6t0dqHzUPHhcPSTQffU68X0l 21tvx9Getpu3NP+RMlVh0HwmcZXqMYx02NKcwEDWirGyJQZEGkkx/I6hz7zXG6GubQwd Qit3bGDlPF4DlQCbEifS1OqoeMsL0w1i6sfuC73NQ9lVkUygvizXboKAKtuzzCc1FjwB t47ah7co8+eutBXGnBVq41V3J2VtYo2pI+swshJf43XEPgJlji+2S+/jGQscjAf9yfCs YWFdRxefXNIOaScL/smsLDOpzwvyffCxopVyRpBBZT1JzgHnxof5lPpx3mnk0e6GQRTn ouYA== X-Gm-Message-State: ACrzQf0SKTXHFVSBDF03yBQaBu/7Eb8Cjs2fIxEwNzPR2swfZ+kszfAb c+Jy4/OANFCMVETM7K5vHb43uWgu7QrmjA== X-Google-Smtp-Source: AMsMyM4pV8NHWIEwjJS69o/OmV0HUECe6P8KknLlVHAsYIYC4Dfxg1lkV2Mfvx/hOkcIzm80PmhVSQ== X-Received: by 2002:a05:600c:4f46:b0:3c6:fb4f:3e1b with SMTP id m6-20020a05600c4f4600b003c6fb4f3e1bmr9922108wmq.159.1666280151918; Thu, 20 Oct 2022 08:35:51 -0700 (PDT) Received: from localhost.localdomain ([46.248.82.114]) by smtp.gmail.com with ESMTPSA id u11-20020adff88b000000b0022e2eaa2bdcsm16486515wrp.98.2022.10.20.08.35.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Oct 2022 08:35:51 -0700 (PDT) From: Uros Bizjak To: linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Uros Bizjak , Christoph Hellwig , Sagi Grimberg , Chaitanya Kulkarni Subject: [PATCH] nvmet: use try_cmpxchg in nvmet_update_sq_head Date: Thu, 20 Oct 2022 17:35:40 +0200 Message-Id: <20221020153540.8226-1-ubizjak@gmail.com> X-Mailer: git-send-email 2.37.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20221020_083555_962088_0AAB8A4B X-CRM114-Status: GOOD ( 13.64 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in nvmet_update_sq_head. 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, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. Note that the value from *ptr should be read using READ_ONCE to prevent the compiler from merging, refetching or reordering the read. No functional change intended. Cc: Christoph Hellwig Cc: Sagi Grimberg Cc: Chaitanya Kulkarni Signed-off-by: Uros Bizjak --- drivers/nvme/target/core.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/nvme/target/core.c b/drivers/nvme/target/core.c index 14677145bbba..a384a0927aed 100644 --- a/drivers/nvme/target/core.c +++ b/drivers/nvme/target/core.c @@ -695,11 +695,10 @@ static void nvmet_update_sq_head(struct nvmet_req *req) if (req->sq->size) { u32 old_sqhd, new_sqhd; + old_sqhd = READ_ONCE(req->sq->sqhd); do { - old_sqhd = req->sq->sqhd; new_sqhd = (old_sqhd + 1) % req->sq->size; - } while (cmpxchg(&req->sq->sqhd, old_sqhd, new_sqhd) != - old_sqhd); + } while (!try_cmpxchg(&req->sq->sqhd, &old_sqhd, new_sqhd)); } req->cqe->sq_head = cpu_to_le16(req->sq->sqhd & 0x0000FFFF); } -- 2.37.3