linux-kernel - Re: [PATCH v2 rdma-next] RDMA/mlx5: Enable Relaxed Ordering by default for kernel ULPs

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Date:   Thu, 10 Jun 2021 10:44:55 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Christoph Hellwig <hch@....de>, Jason Gunthorpe <jgg@...dia.com>
Cc:     Doug Ledford <dledford@...hat.com>,
        Avihai Horon <avihaih@...dia.com>,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Bart Van Assche <bvanassche@....org>,
        Tom Talpey <tom@...pey.com>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        Chuck Lever III <chuck.lever@...cle.com>,
        Keith Busch <kbusch@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Honggang LI <honli@...hat.com>,
        Max Gurtovoy <mgurtovoy@...dia.com>
Subject: Re: [PATCH v2 rdma-next] RDMA/mlx5: Enable Relaxed Ordering by
 default for kernel ULPs

On Wed, Jun 09, 2021 at 03:59:24PM +0200, Christoph Hellwig wrote:
> On Wed, Jun 09, 2021 at 04:53:23PM +0300, Leon Romanovsky wrote:
> > Sure, did you have in mind some concrete place? Or will new file in the
> > Documentation/infiniband/ folder be good enough too?
> 
> Maybe add a kerneldoc comment for the map_mr_sg() ib_device_ops method?

I hope that this hunk from the previous cover letter is good enough.

Jason, do you want v3? or you can fold this into v2?

diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
index 9423e70a881c..aaf63a6643d6 100644
--- a/include/rdma/ib_verbs.h
+++ b/include/rdma/ib_verbs.h
@@ -2468,6 +2468,13 @@ struct ib_device_ops {
                         enum ib_uverbs_advise_mr_advice advice, u32 flags,
                         struct ib_sge *sg_list, u32 num_sge,
                         struct uverbs_attr_bundle *attrs);
+       /*
+        * Kernel users should universally support relaxed ordering (RO),
+        * as they are designed to read data only after observing the CQE
+        * and use the DMA API correctly.
+        *
+        * Some drivers implicitly enable RO if platform supports it.
+        */
        int (*map_mr_sg)(struct ib_mr *mr, struct scatterlist *sg, int sg_nents,
                         unsigned int *sg_offset);
        int (*check_mr_status)(struct ib_mr *mr, u32 check_mask,