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From: Leon Romanovsky <leon@kernel.org>
To: liweihang <liweihang@huawei.com>
Cc: "jgg@ziepe.ca" <jgg@ziepe.ca>,
	"dledford@redhat.com" <dledford@redhat.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
	Linuxarm <linuxarm@huawei.com>
Subject: Re: Questions about masked atomic
Date: Tue, 12 May 2020 14:35:12 +0300	[thread overview]
Message-ID: <20200512113512.GK4814@unreal> (raw)
In-Reply-To: <B82435381E3B2943AA4D2826ADEF0B3A02359ED3@DGGEML522-MBX.china.huawei.com>

On Mon, May 11, 2020 at 01:54:48PM +0000, liweihang wrote:
> Hi All,
>
> I have two questions about masked atomic (Masked Compare and Swap & MFetchAdd):
>
> 1. The kernel now supports masked atomic, but the it does not support atomic
>    operation. Is the masked atomic valid in kernel currently?

Yes, it is valid, but probably has a very little real value for the kernel ULPs.
I see code in the RDS that uses atomics, but it says nothing to me, because
upstream RDS and version in-real-use are completely different.

> 2. In the userspace, ofed does not have the corresponding opcode for the masked
>    atomic (IB_WR_MASKED_ATOMIC_CMP_AND_SWP, IB_WR_MASKED_ATOMIC_FETCH_AND_ADD),
>    and ibv_send_wr also has no related data segment for it. How to support it in
>    userspace?

ibv_send_wr is not extensible, so the real solution will need to extend ibv_wr_post() [1]
with specific and new post builders.

Thanks

[1] https://github.com/linux-rdma/rdma-core/blob/master/libibverbs/man/ibv_wr_post.3.md

>
> Thanks
> Weihang

  reply	other threads:[~2020-05-12 11:35 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-11 13:54 Questions about masked atomic liweihang
2020-05-12 11:35 ` Leon Romanovsky [this message]
2020-05-15  9:40   ` liweihang
2020-05-17 13:14     ` Leon Romanovsky
2020-05-17 18:58       ` Tom Talpey
2020-05-19  1:27         ` liweihang

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