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SubjectRe: [PATCH v6] RDMA/qedr: eliminate duplicate barriers on weakly-ordered archs #2
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On 3/22/2018 12:30 PM, Sinan Kaya wrote:
> Code includes wmb() followed by writel() in multiple places. 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 <okaya@codeaurora.org>
> ---
> drivers/infiniband/hw/qedr/verbs.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/hw/qedr/verbs.c b/drivers/infiniband/hw/qedr/verbs.c
> index 53f00db..d1cf9a0 100644
> --- a/drivers/infiniband/hw/qedr/verbs.c
> +++ b/drivers/infiniband/hw/qedr/verbs.c
> @@ -35,6 +35,7 @@
> #include <net/ipv6.h>
> #include <net/udp.h>
> #include <linux/iommu.h>
> +#include <linux/io-64-nonatomic-hi-lo.h>

what should we do here? change include? drop writeq_relaxed?

>
> #include <rdma/ib_verbs.h>
> #include <rdma/ib_user_verbs.h>
> @@ -860,7 +861,7 @@ 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);
>
> /* Make sure write would stick */
> mmiowb();
> @@ -3338,7 +3339,7 @@ int qedr_post_recv(struct ib_qp *ibqp, struct ib_recv_wr *wr,
>
> qp->rq.db_data.data.value++;
>
> - writel(qp->rq.db_data.raw, qp->rq.db);
> + writel_relaxed(qp->rq.db_data.raw, qp->rq.db);
>
> /* Make sure write sticks */
> mmiowb();
>


--
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.

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