From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Gunthorpe Subject: Re: [PATCH v4 2/6] IB/mlx4: Eliminate duplicate barriers on weakly-ordered archs Date: Tue, 20 Mar 2018 08:48:51 -0600 Message-ID: <20180320144851.GF19744@ziepe.ca> References: <1521514068-8856-1-git-send-email-okaya@codeaurora.org> <1521514068-8856-3-git-send-email-okaya@codeaurora.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1521514068-8856-3-git-send-email-okaya@codeaurora.org> Sender: linux-kernel-owner@vger.kernel.org To: Sinan Kaya Cc: linux-rdma@vger.kernel.org, timur@codeaurora.org, sulrich@codeaurora.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Yishai Hadas , Doug Ledford , linux-kernel@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org On Mon, Mar 19, 2018 at 10:47:44PM -0400, Sinan Kaya wrote: > Code includes wmb() followed by writel(). writel() already has a barrier on > some architectures like arm64. > > This ends up CPU observing two barriers back to back before executing the > register write. > > Since code already has an explicit barrier call, changing writel() to > writel_relaxed(). > > Signed-off-by: Sinan Kaya > --- > drivers/infiniband/hw/mlx4/qp.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Reviewed-by: Jason Gunthorpe > diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c > index f045491..74b27b0 100644 > --- a/drivers/infiniband/hw/mlx4/qp.c > +++ b/drivers/infiniband/hw/mlx4/qp.c > @@ -3880,8 +3880,8 @@ int mlx4_ib_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr, > */ > wmb(); > > - writel(qp->doorbell_qpn, > - to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL); > + writel_relaxed(qp->doorbell_qpn, > + to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL); > > /* > * Make sure doorbells don't leak out of SQ spinlock > -- > 2.7.4 > From mboxrd@z Thu Jan 1 00:00:00 1970 From: jgg@ziepe.ca (Jason Gunthorpe) Date: Tue, 20 Mar 2018 08:48:51 -0600 Subject: [PATCH v4 2/6] IB/mlx4: Eliminate duplicate barriers on weakly-ordered archs In-Reply-To: <1521514068-8856-3-git-send-email-okaya@codeaurora.org> References: <1521514068-8856-1-git-send-email-okaya@codeaurora.org> <1521514068-8856-3-git-send-email-okaya@codeaurora.org> Message-ID: <20180320144851.GF19744@ziepe.ca> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Mar 19, 2018 at 10:47:44PM -0400, Sinan Kaya wrote: > Code includes wmb() followed by writel(). writel() already has a barrier on > some architectures like arm64. > > This ends up CPU observing two barriers back to back before executing the > register write. > > Since code already has an explicit barrier call, changing writel() to > writel_relaxed(). > > Signed-off-by: Sinan Kaya > --- > drivers/infiniband/hw/mlx4/qp.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) Reviewed-by: Jason Gunthorpe > diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c > index f045491..74b27b0 100644 > --- a/drivers/infiniband/hw/mlx4/qp.c > +++ b/drivers/infiniband/hw/mlx4/qp.c > @@ -3880,8 +3880,8 @@ int mlx4_ib_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr, > */ > wmb(); > > - writel(qp->doorbell_qpn, > - to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL); > + writel_relaxed(qp->doorbell_qpn, > + to_mdev(ibqp->device)->uar_map + MLX4_SEND_DOORBELL); > > /* > * Make sure doorbells don't leak out of SQ spinlock > -- > 2.7.4 >