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=-2.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 B200DC28CBC for ; Wed, 6 May 2020 14:44:42 +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 79C23208CA for ; Wed, 6 May 2020 14:44:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="u4QmC7lZ"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="g8SkUGNK" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 79C23208CA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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=gc/5EC+QzfOYpnbdBZpMPnREScZmNggnKDPbGpk1agw=; b=u4QmC7lZMjQj31 tpJhj9GpvjjFyKmJ+B2Qt+L7I38upd+7nerzg5u2PWR1AlJCy0YKp3N7jd9/95BQTgbufyKV6hhYF hmlIchc9miGej02Ohrghu9LB4zFPgZo78CCOH0uyPA/4T4eg4so1aQRblOVJJlnu4orJg5FSGz5aA QKECoKl1m45F1j7C9CGQeluZA/OQ2Wj71qbVv5kHyUFkWb2bO4Q2Py9qBdLwg7wcbwx01UIj4K6GR wq9cxpg/GDl/8AAlfjBoQrLzw+uZXWTbpSsRgX9iusfwPHzxQ8nsO6vuMMJrWMqE8OD8cHcPWU+N+ YZ56Nte1D2sHJ4gTmV2A==; 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 1jWLHs-0002Rd-Fz; Wed, 06 May 2020 14:44:40 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jWLHq-0002Qx-Iv for linux-nvme@lists.infradead.org; Wed, 06 May 2020 14:44:39 +0000 Received: from C02WT3WMHTD6 (unknown [8.36.226.102]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 967CB2073A; Wed, 6 May 2020 14:44:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1588776275; bh=/farS+W6/FsuN9fPZbVDk0w4G4pOKHKoSTWzsgHI2ik=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=g8SkUGNK73wfzGgfmDInACcCmM2SDRQhX+A/VUYYbaCmIkUcMppnP2WEpNn09cV9n p8BYNHkiqebNXYy/uGitzQ8APP3uXi8dgPMckj8jxW+EMEGpK/y68IQl14YdnL6t5z s5uMqkt6vvglWsMATvkQOZoDvFR1+mqbwSRu44Zo= Date: Wed, 6 May 2020 08:44:34 -0600 From: Keith Busch To: Alexey Dobriyan Subject: Re: [PATCH] nvme-pci: slimmer CQ head update Message-ID: <20200506144434.GB54933@C02WT3WMHTD6> References: <20200228184519.GA2281@avx2> <20200229055351.GA542920@dhcp-10-100-145-180.wdl.wdc.com> <20200506124701.GA54933@C02WT3WMHTD6> <20200506132429.GA21451@avx2> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200506132429.GA21451@avx2> User-Agent: Mutt/1.12.1 (2019-06-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200506_074438_646111_7AD028CC X-CRM114-Status: UNSURE ( 9.69 ) X-CRM114-Notice: Please train this message. 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: axboe@fb.com, John Garry , 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 Wed, May 06, 2020 at 04:24:29PM +0300, Alexey Dobriyan wrote: > static inline void nvme_update_cq_head(struct nvme_queue *nvmeq) > { > - if (++nvmeq->cq_head == nvmeq->q_depth) { > + /* > + * Can't pre-increment ->cq_head directly. > + * It must be in [0, ->q_depth) range at all times. > + */ > + u16 tmp = READ_ONCE(nvmeq->cq_head); > + if (++tmp == nvmeq->q_depth) { This looks correct too, but there's no need for the READ_ONCE access, or the pre-increment: u16 tmp = nvmeq->cq_head + 1; if (tmp == nvmeq->q_depth) { _______________________________________________ linux-nvme mailing list linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme