linux-kernel - Re: [PATCH v4 00/14] mpt3sas driver NVMe support:

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Message-ID: <yq13787w1a3.fsf@oracle.com>
Date:   Thu, 31 Aug 2017 23:22:44 -0400
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-scsi@...r.kernel.org,
        Sathya Prakash <Sathya.Prakash@...adcom.com>,
        Kashyap Desai <kashyap.desai@...adcom.com>,
        linux-kernel@...r.kernel.org,
        Chaitra Basappa <chaitra.basappa@...adcom.com>,
        Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
        linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v4 00/14] mpt3sas driver NVMe support:


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