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From: Weihang Li <liweihang@huawei.com>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: <dledford@redhat.com>, <leon@kernel.org>,
	<linux-rdma@vger.kernel.org>, <linuxarm@huawei.com>
Subject: Re: [PATCH for-next] RDMA/hns: Add support for extended atomic in userspace
Date: Wed, 22 Jan 2020 16:54:55 +0800	[thread overview]
Message-ID: <cebc88dc-09fe-a1dd-a3da-a3de55deb732@huawei.com> (raw)
In-Reply-To: <20200116195118.GG10759@ziepe.ca>



On 2020/1/17 3:51, Jason Gunthorpe wrote:
>>> What happens to your userspace if it runs on an old kernel and tries
>>> to use extended atomic?
>>>
>>> Jason
>>>
>> Hi Jason,
>>
>> If the hns userspace runs with old kernel, the hardware will report a asynchronous
>> event for the extended atomic operation and modify the qp to error state because
>> the enable bit in this qp's context hasn't been set.
>>
>> The driver will print like this:
>>
>> [ 1252.240921] hns3 0000:7d:00.0: Invalid request local work queue 0x9 error.
>> [ 1252.247772] hns3 0000:7d:00.0: no hr_qp can be found!
> Ideally the provider will not set
> IBV_PCI_ATOMIC_OPERATION_4_BYTE_SIZE_SUP and related without kernel
> support..
> 
> I've applied this patch, but I feel like you may need a followup to
> fix the capability reporting?
> 
> Jason

Hi Jason,

Thank for your suggestions.

But I'm confuse about the relationship between "PCI ATOMIC" in this macro
and atomic operations in RDMA.

I found the related series on patchwork:
https://patchwork.kernel.org/cover/10782873/

And I found the description about atomic operations in PCIe specification
v4.0:

"An Atomic Operation (AtomicOp) is a single PCI Express transaction that
targets a location in Memory Space, reads the location’s value, potentially
writes a new value back to the location, and returns the original value. This
"read-modify-write" sequence to the location is performed atomically."

It seems that the atomic for PCIe and RDMA is different concepts, and the macro
IBV_PCI_ATOMIC_OPERATION_4_BYTE_SIZE_SUP is for PCIe atomic.

Could you please give me more suggestions about them?

Thanks
Weihang


  reply	other threads:[~2020-01-22  8:55 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-15  1:42 [PATCH for-next] RDMA/hns: Add support for extended atomic in userspace Weihang Li
2020-01-15 20:56 ` Jason Gunthorpe
2020-01-16  4:05   ` Weihang Li
2020-01-16 19:51     ` Jason Gunthorpe
2020-01-22  8:54       ` Weihang Li [this message]
2020-01-22 14:08         ` Tom Talpey
2020-01-26  3:38           ` Weihang Li
2020-01-23 22:54         ` Jason Gunthorpe
2020-01-26  3:42           ` Weihang Li

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