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Date:   Wed, 4 Apr 2018 08:30:27 -0600
From:   Keith Busch <keith.busch@intel.com>
To:     "Eric H. Chang" <echang@sk.com>
Cc:     Christoph Hellwig <hch@lst.de>, Baegjae Sung <baegjae@gmail.com>,
        "axboe@fb.com" <axboe@fb.com>,
        "sagi@grimberg.me" <sagi@grimberg.me>,
        "linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] nvme-multipath: implement active-active round-robin
        path selector
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On Fri, Mar 30, 2018 at 09:04:46AM +0000, Eric H. Chang wrote:
> We internally call PCIe-retimer as HBA. It's not a real Host Bus Adapter that translates the interface from PCIe to SATA or SAS. Sorry for the confusion.

Please don't call a PCIe retimer an "HBA"! :)

While your experiment is setup to benefit from round-robin, my only
concern is it has odd performance in a real world scenario with
IO threads executing in different nodes. Christoph's proposal will
naturally utilize both paths optimally there, where round-robin will
saturate node interlinks.

Not that I'm against having the choice; your setup probably does represent
real use. But if we're going to have multiple choice, user documentation
on nvme path selectors will be useful here.