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From: Tom Talpey <tom@talpey.com>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Chuck Lever III <chuck.lever@oracle.com>,
	Christoph Hellwig <hch@lst.de>, Leon Romanovsky <leon@kernel.org>,
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Subject: Re: [PATCH rdma-next 00/10] Enable relaxed ordering for ULPs
Date: Fri, 9 Apr 2021 13:44:23 -0400
Message-ID: <70909c83-5e3a-6cb5-a8c0-6bd2a6688fb4@talpey.com> (raw)
In-Reply-To: <20210409164046.GY7405@nvidia.com>

On 4/9/2021 12:40 PM, Jason Gunthorpe wrote:
> On Fri, Apr 09, 2021 at 10:26:21AM -0400, Tom Talpey wrote:
> 
>> My belief is that the biggest risk is from situations where completions
>> are batched, and therefore polling is used to detect them without
>> interrupts (which explicitly).
> 
> We don't do this in the kernel.
> 
> All kernel ULPs only read data after they observe the CQE. We do not
> have "last data polling" and our interrupt model does not support some
> hacky "interrupt means go and use the data" approach.
> 
> ULPs have to be designed this way to use the DMA API properly.

Yep. Totally agree.

My concern was about the data being written as relaxed, and the CQE
racing it. I'll reply in the other fork.


> Fencing a DMA before it is completed by the HW will cause IOMMU
> errors.
> 
> Userspace is a different story, but that will remain as-is with
> optional relaxed ordering.
> 
> Jason
> 

  reply index

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-05  5:23 Leon Romanovsky
2021-04-05  5:23 ` [PATCH rdma-next 01/10] RDMA: Add access flags to ib_alloc_mr() and ib_mr_pool_init() Leon Romanovsky
2021-04-05 13:46   ` Christoph Hellwig
2021-04-06  5:24     ` Leon Romanovsky
2021-04-05 15:27   ` Bart Van Assche
2021-04-06  5:23     ` Leon Romanovsky
2021-04-06  5:27       ` Christoph Hellwig
2021-04-06  5:58         ` Leon Romanovsky
2021-04-06 12:13           ` Jason Gunthorpe
2021-04-06 12:30             ` Christoph Hellwig
2021-04-06 14:04               ` Jason Gunthorpe
2021-04-06 14:15                 ` Christoph Hellwig
2021-04-06 14:40                   ` Jason Gunthorpe
2021-04-06 14:54                     ` Christoph Hellwig
2021-04-06 15:03                       ` Christoph Hellwig
2021-04-07 18:28                       ` Jason Gunthorpe
2021-04-05  5:23 ` [PATCH rdma-next 02/10] RDMA/core: Enable Relaxed Ordering in __ib_alloc_pd() Leon Romanovsky
2021-04-05 18:01   ` Tom Talpey
2021-04-05 20:40     ` Adit Ranadive
2021-04-06  6:28     ` Leon Romanovsky
2021-04-05  5:23 ` [PATCH rdma-next 03/10] RDMA/iser: Enable Relaxed Ordering Leon Romanovsky
2021-04-05  5:23 ` [PATCH rdma-next 04/10] RDMA/rtrs: " Leon Romanovsky
2021-04-05  5:23 ` [PATCH rdma-next 05/10] RDMA/srp: " Leon Romanovsky
2021-04-05  5:24 ` [PATCH rdma-next 06/10] nvme-rdma: " Leon Romanovsky
2021-04-05  5:24 ` [PATCH rdma-next 07/10] cifs: smbd: " Leon Romanovsky
2021-04-05  5:24 ` [PATCH rdma-next 08/10] net/rds: " Leon Romanovsky
2021-04-05  5:24 ` [PATCH rdma-next 09/10] net/smc: " Leon Romanovsky
2021-04-05  5:24 ` [PATCH rdma-next 10/10] xprtrdma: " Leon Romanovsky
2021-04-05 13:41 ` [PATCH rdma-next 00/10] Enable relaxed ordering for ULPs Christoph Hellwig
2021-04-05 14:08   ` Leon Romanovsky
2021-04-05 16:11     ` Santosh Shilimkar
2021-04-05 17:54     ` Tom Talpey
2021-04-05 20:07   ` Jason Gunthorpe
2021-04-05 23:42     ` Chuck Lever III
2021-04-05 23:50       ` Keith Busch
2021-04-06  5:12       ` Leon Romanovsky
2021-04-06 11:49       ` Jason Gunthorpe
2021-04-09 14:26         ` Tom Talpey
2021-04-09 14:45           ` Chuck Lever III
2021-04-09 15:32             ` Tom Talpey
2021-04-09 16:27               ` Haakon Bugge
2021-04-09 17:49                 ` Tom Talpey
2021-04-10 13:30                   ` David Laight
2021-04-12 18:32                     ` Haakon Bugge
2021-04-12 20:20                       ` Tom Talpey
2021-04-12 22:48                         ` Jason Gunthorpe
2021-04-14 14:16                           ` Tom Talpey
2021-04-14 14:41                             ` David Laight
2021-04-14 14:49                               ` Jason Gunthorpe
2021-04-14 14:44                             ` Jason Gunthorpe
2021-04-09 16:40           ` Jason Gunthorpe
2021-04-09 17:44             ` Tom Talpey [this message]
2021-04-06  2:37 ` Honggang LI
2021-04-06  5:09   ` Leon Romanovsky
2021-04-06 11:53     ` Jason Gunthorpe
2021-04-11 10:09       ` Max Gurtovoy

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