netdev - Re: [PATCH rdma-next 00/10] Enable relaxed ordering for ULPs

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Message-ID: <20210405134115.GA22346@lst.de>
Date:   Mon, 5 Apr 2021 15:41:15 +0200
From:   Christoph Hellwig <hch@....de>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Leon Romanovsky <leonro@...dia.com>,
        Adit Ranadive <aditr@...are.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Ariel Elior <aelior@...vell.com>,
        Avihai Horon <avihaih@...dia.com>,
        Bart Van Assche <bvanassche@....org>,
        Bernard Metzler <bmt@...ich.ibm.com>,
        Christoph Hellwig <hch@....de>,
        Chuck Lever <chuck.lever@...cle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Devesh Sharma <devesh.sharma@...adcom.com>,
        Faisal Latif <faisal.latif@...el.com>,
        Jack Wang <jinpu.wang@...os.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Jens Axboe <axboe@...com>,
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        rds-devel@....oracle.com, Sagi Grimberg <sagi@...mberg.me>,
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        Weihang Li <liweihang@...wei.com>,
        Yishai Hadas <yishaih@...dia.com>,
        Zhu Yanjun <zyjzyj2000@...il.com>
Subject: Re: [PATCH rdma-next 00/10] Enable relaxed ordering for ULPs

On Mon, Apr 05, 2021 at 08:23:54AM +0300, Leon Romanovsky wrote:
> From: Leon Romanovsky <leonro@...dia.com>
> 
> >From Avihai,
> 
> Relaxed Ordering is a PCIe mechanism that relaxes the strict ordering
> imposed on PCI transactions, and thus, can improve performance.
> 
> Until now, relaxed ordering could be set only by user space applications
> for user MRs. The following patch series enables relaxed ordering for the
> kernel ULPs as well. Relaxed ordering is an optional capability, and as
> such, it is ignored by vendors that don't support it.
> 
> The following test results show the performance improvement achieved
> with relaxed ordering. The test was performed on a NVIDIA A100 in order
> to check performance of storage infrastructure over xprtrdma:

Isn't the Nvidia A100 a GPU not actually supported by Linux at all?
What does that have to do with storage protocols?

Also if you enable this for basically all kernel ULPs, why not have
an opt-out into strict ordering for the cases that need it (if there are
any).