From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sinan Kaya Subject: Re: [PATCH v5 3/3] RDMA/qedr: eliminate duplicate barriers on weakly-ordered archs #2 Date: Mon, 2 Apr 2018 22:29:53 -0400 Message-ID: References: <1521736009-23387-1-git-send-email-okaya@codeaurora.org> <1521736009-23387-4-git-send-email-okaya@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1521736009-23387-4-git-send-email-okaya@codeaurora.org> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: linux-rdma@vger.kernel.org, timur@codeaurora.org, sulrich@codeaurora.org Cc: linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Michal Kalderon , Ariel Elior , Doug Ledford , Jason Gunthorpe , linux-kernel@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org On 3/22/2018 12:26 PM, Sinan Kaya wrote: > @@ -860,7 +860,7 @@ static void doorbell_cq(struct qedr_cq *cq, u32 cons, u8 flags) > wmb(); > cq->db.data.agg_flags = flags; > cq->db.data.value = cpu_to_le32(cons); > - writeq(cq->db.raw, cq->db_addr); > + writeq_relaxed(cq->db.raw, cq->db_addr); Given the direction to get rid of wmb() in front of writeX() functions, I have been reviewing this code. Under normal circumstances, I can get rid of all wmb() as follows. However, I started having my doubts now. Are these wmb() used as a SMP barrier too? I can't find any smp_Xmb() in drivers/infiniband/hw/qedr directory. static void doorbell_cq(struct qedr_cq *cq, u32 cons, u8 flags) { - /* Flush data before signalling doorbell */ - wmb(); cq->db.data.agg_flags = flags; cq->db.data.value = cpu_to_le32(cons); writeq(cq->db.raw, cq->db_addr); @@ -1870,8 +1868,7 @@ static int qedr_update_qp_state(struct qedr_dev *dev, */ if (rdma_protocol_roce(&dev->ibdev, 1)) { - wmb(); - writel_relaxed(qp->rq.db_data.raw, qp->rq.db); + writel(qp->rq.db_data.raw, qp->rq.db); /* Make sure write takes effect */ mmiowb(); } @@ -3275,8 +3272,7 @@ int qedr_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr, * unchanged). For performance reasons we avoid checking for this * redundant doorbell. */ - wmb(); - writel_relaxed(qp->sq.db_data.raw, qp->sq.db); + writel(qp->sq.db_data.raw, qp->sq.db); /* Make sure write sticks */ mmiowb(); @@ -3362,9 +3358,6 @@ int qedr_post_recv(struct ib_qp *ibqp, struct ib_recv_wr *wr, qedr_inc_sw_prod(&qp->rq); - /* Flush all the writes before signalling doorbell */ - wmb(); -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.