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    SubjectRe: [PATCH v4 00/14] mpt3sas driver NVMe support:
    Hi Martin,

    On Fri, Sep 15, 2017 at 6:37 AM, Martin K. Petersen
    <martin.petersen@oracle.com> wrote:
    >
    > Suganath,
    >
    >> Is there any update on the submitted mpt3sas patches.
    >
    > We are waiting for you to report back your findings on PRP vs. SGL.

    We are working on this, since there is h/w dependent, we are in
    discussion with H/W & F/W team and doing experiments. If there is no
    impact, and if SGL translation has to be removed, this change has to
    go through some phase of testing, before we post it to upstream, since
    that is not inline with H/W requirement.

    The hardware translation of IEEE SGL to NVMe PRPs has limitation.

    We have added the below comment in patch 3 as well:

    if a command cannot be translated by hardware then it will go
    to firmware and the firmware needs to translate it. And this will
    have a performance reduction. To avoid that driver proactively
    checks whether the translation will be done in hardware or not,
    if not then driver try to translate inside the driver

    Current code posted to upstream is inline with hardware requirements
    and well tested internally.

    SGL vs NVMe PRP building in driver is small sanity check for decision making
    and it is not going to change in long run.

    Also, Making all PRP buffer may or may not need FW changes (assuming
    it is possible.),
    we may end up into multiple FW version check.

    Since this is main IO path and current driver is following H/W limitation,
    we should avoid any changes in this area until and unless change is
    universal acceptable in FW (for all type of work load).

    Hope this clarifies.
    >
    > --
    > Martin K. Petersen Oracle Linux Engineering

    Thanks,
    Suganath Prabu S

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