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 X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 96D2DC83000 for ; Tue, 28 Apr 2020 07:08:58 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 66AF4206A5 for ; Tue, 28 Apr 2020 07:08:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="C/HoR0o0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 66AF4206A5 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=SEeaCyOJtmruW+xNJyeJ5iShbz9fq9Sw1xm37MJyItI=; b=C/HoR0o0TUte+z bSXdeDGg58KEmHPg6whE5OJMj5sVZxUW+KNfMw9uXNc6bE+AnCaT8kAMjpea/rvW+8sYuhgwjz66F XFchtnBpYOn8C7nfkJI46v9ymJs7mhWYRcud+Fr4nl82LRLAGyVyaewDis2C53vhz7JlnYJKq128J c5eeWKMoPAHNApekZ8wXftb5YVQ2umMzZ/b0bFhxpMV5Zk4HkQvZJL2MgZpwITF5XquY+N/BaO0L5 DDDUBTXiK2WKnn3KULCPD5AMGhgu5Sqit9M+Ul4URjqV4sCnjeOSYkuI2G8pkQ84LQsyZstsPF30I 1uyoLm/oObFxpoZCSrtg==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jTKMT-0003cM-3Z; Tue, 28 Apr 2020 07:08:57 +0000 Received: from verein.lst.de ([213.95.11.211]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jTKMQ-0003bu-MC for linux-nvme@lists.infradead.org; Tue, 28 Apr 2020 07:08:56 +0000 Received: by verein.lst.de (Postfix, from userid 2407) id 7117368CEC; Tue, 28 Apr 2020 09:08:48 +0200 (CEST) Date: Tue, 28 Apr 2020 09:08:48 +0200 From: Christoph Hellwig To: Keith Busch Subject: Re: [PATCH] nvme-pci: remove volatile cqes Message-ID: <20200428070848.GD18754@lst.de> References: <20200427191446.2195863-1-kbusch@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200427191446.2195863-1-kbusch@kernel.org> User-Agent: Mutt/1.5.17 (2007-11-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200428_000854_872909_84F24870 X-CRM114-Status: GOOD ( 14.36 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: hch@lst.de, linux-nvme@lists.infradead.org, sagi@grimberg.me Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Mon, Apr 27, 2020 at 12:14:46PM -0700, Keith Busch wrote: > The completion queue entry is not volatile once the phase is confirmed. > Remove the volaitle keywords and check the phase using the appropriate > READ_ONCE() accessor, allowing the compiler to optimize the remaining > completion path. > > Signed-off-by: Keith Busch > --- > drivers/nvme/host/pci.c | 9 +++++---- > 1 file changed, 5 insertions(+), 4 deletions(-) > > diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c > index 8ebcf40f04fe..cf386c84588b 100644 > --- a/drivers/nvme/host/pci.c > +++ b/drivers/nvme/host/pci.c > @@ -166,7 +166,7 @@ struct nvme_queue { > void *sq_cmds; > /* only used for poll queues: */ > spinlock_t cq_poll_lock ____cacheline_aligned_in_smp; > - volatile struct nvme_completion *cqes; > + struct nvme_completion *cqes; > dma_addr_t sq_dma_addr; > dma_addr_t cq_dma_addr; > u32 __iomem *q_db; > @@ -908,8 +908,9 @@ static void nvme_pci_complete_rq(struct request *req) > /* We read the CQE phase first to check if the rest of the entry is valid */ > static inline bool nvme_cqe_pending(struct nvme_queue *nvmeq) > { > - return (le16_to_cpu(nvmeq->cqes[nvmeq->cq_head].status) & 1) == > - nvmeq->cq_phase; > + return (le16_to_cpu( > + READ_ONCE(nvmeq->cqes[nvmeq->cq_head].status)) & 1) == > + nvmeq->cq_phase; Despite the sound logic this just visually looks horrible. How about: static inline bool nvme_cqe_pending(struct nvme_queue *nvmeq) { struct nvme_completion *hcqe = &nvmeq->cqes[nvmeq->cq_head]; return (le16_to_cpu(READ_ONCE(hcqe->status)) & 1) == nvmeq->cq_phase; } Otherwise looks fine: Reviewed-by: Christoph Hellwig _______________________________________________ linux-nvme mailing list linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme