netdev - Re: [PATCH rdma-next v2 2/3] RDMA/rw: Support threshold for registration vs scattering to local pages

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Date:   Mon, 7 Oct 2019 15:22:30 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Christoph Hellwig <hch@...radead.org>,
        RDMA mailing list <linux-rdma@...r.kernel.org>,
        Or Gerlitz <ogerlitz@...lanox.com>,
        Yamin Friedman <yaminf@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>,
        linux-netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH rdma-next v2 2/3] RDMA/rw: Support threshold for
 registration vs scattering to local pages

On 10/7/19 9:03 AM, Leon Romanovsky wrote:
> On Mon, Oct 07, 2019 at 08:07:55AM -0700, Bart Van Assche wrote:
>> On 10/7/19 6:59 AM, Leon Romanovsky wrote:
>>>    /*
>>> - * Check if the device might use memory registration.  This is currently only
>>> - * true for iWarp devices. In the future we can hopefully fine tune this based
>>> - * on HCA driver input.
>>> + * Check if the device might use memory registration. This is currently
>>> + * true for iWarp devices and devices that have optimized SGL registration
>>> + * logic.
>>>     */
>>
>> The following sentence in the above comment looks confusing to me: "Check if
>> the device might use memory registration." That sentence suggests that the
>> HCA decides whether or not to use memory registration. Isn't it the RDMA R/W
>> code that decides whether or not to use memory registration?
> 
> I'm open for any reasonable text, what do you expect to be written there?

Hi Leon,

How about the following (not sure whether this is correct)?

/*
  * Report whether memory registration should be used. Memory
  * registration must be used for iWarp devices because of
  * iWARP-specific limitations. Memory registration is also enabled if
  * registering memory will yield better performance than using multiple
  * SGE entries.
  */

Thanks,

Bart.