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To: Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>,
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Subject: Re: [PATCH v4 00/14] mpt3sas driver NVMe support:
From: "Martin K. Petersen" <martin.petersen@oracle.com>
Organization: Oracle Corporation
References: <1503322344-5900-1-git-send-email-suganath-prabu.subramani@broadcom.com>
        <yq1lgmbauxt.fsf@oracle.com>
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        <CA+RiK67f59U5Ss_Z2=veBRODtBSp1-4VTbosLkHkgaxY9XA6hQ@mail.gmail.com>
Date: Thu, 31 Aug 2017 23:22:44 -0400
In-Reply-To: <CA+RiK67f59U5Ss_Z2=veBRODtBSp1-4VTbosLkHkgaxY9XA6hQ@mail.gmail.com>
        (Suganath Prabu Subramani's message of "Thu, 31 Aug 2017 10:28:06
        +0530")
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Hi Suganath,

> Let me explain - NVME device fast path is possible in two ways.  IEEE
> SGL and PRP SGL. Due to h/w constraint we choose IEEE SGL only for
> smaller IO size.  Both above is true h/w Fast Path and no firmware
> involvement.

> Agree with you. We are planning to see if we can keep only simple Fast
> Path using only PRP.

That would be great, thank you!

> Currently there is no performance issue for UNMAP translation in FW.

Good!

>> And yet patch 4 circumvents that statement by adding support for
>> encapsulated commands to bypass the FW translation...
>
> This path is not due to performance reason. User wants to interact
> with NVME drive in native NVME command for management.

Patch 4 states:

"This encapsulated NVMe command is used by applications to send direct
NVMe commands to NVMe drives or for handling unmap where the translation
at controller/firmware level is having performance issues."

-- 
Martin K. Petersen	Oracle Linux Engineering