From: Sagi Grimberg <sagi@grimberg.me>
To: Christoph Hellwig <hch@lst.de>
Cc: Kanchan Joshi <joshi.k@samsung.com>,
kbusch@kernel.org, axboe@kernel.dk, io-uring@vger.kernel.org,
linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
asml.silence@gmail.com, joshiiitr@gmail.com,
anuj20.g@samsung.com, gost.dev@samsung.com
Subject: Re: [PATCH for-next 4/4] nvme-multipath: add multipathing for uring-passthrough commands
Date: Wed, 13 Jul 2022 11:04:31 +0300 [thread overview]
Message-ID: <24f0a3e6-aa53-8c69-71b7-d66289a63eae@grimberg.me> (raw)
In-Reply-To: <20220713053633.GA13135@lst.de>
>> I think the difference from scsi-generic and controller nvme passthru is
>> that this is a mpath device node (or mpath chardev). This is why I think
>> that users would expect that it would have equivalent multipath
>> capabilities (i.e. failover).
>
> How is that different from /dev/sg?
/dev/sg it is not a multipath device.
Maybe the solution is to just not expose a /dev/ng for the mpath device
node, but only for bottom namespaces. Then it would be completely
equivalent to scsi-generic devices.
It just creates an unexpected mix of semantics of best-effort
multipathing with just path selection, but no requeue/failover...
>> In general, I think that uring passthru as an alternative I/O interface
>> and as such needs to be able to failover. If this is not expected from
>> the interface, then why are we exposing a chardev for the mpath device
>> node? why not only the bottom namespaces?
>
> The failover will happen when you retry, but we leave that retry to
> userspace. There even is the uevent to tell userspace when a new
> path is up.
If the user needs to do the retry, discover and understand namespace
paths, ANA states, controller states, etc. Why does the user need a
mpath chardev at all?
The user basically needs to understand everything including indirectly
path selection for the I/O. IMO it is cleaner for the user to just have
the bottom devices and do the path selection directly.
next prev parent reply other threads:[~2022-07-13 8:04 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20220711110753epcas5p4169b9e288d15ca35740dbb66a6f6983a@epcas5p4.samsung.com>
2022-07-11 11:01 ` [PATCH for-next 0/4] nvme-multipathing for uring-passthrough Kanchan Joshi
[not found] ` <CGME20220711110800epcas5p3d338dd486fd778c5ba5bfe93a91ec8bd@epcas5p3.samsung.com>
2022-07-11 11:01 ` [PATCH for-next 1/4] io_uring, nvme: rename a function Kanchan Joshi
2022-07-14 13:55 ` Ming Lei
[not found] ` <CGME20220711110812epcas5p33aa90b23aa62fb11722aa8195754becf@epcas5p3.samsung.com>
2022-07-11 11:01 ` [PATCH for-next 2/4] nvme: compact nvme_uring_cmd_pdu struct Kanchan Joshi
2022-07-12 6:32 ` Christoph Hellwig
[not found] ` <CGME20220711110824epcas5p22c8e945cb8c3c3ac46c8c2b5ab55db9b@epcas5p2.samsung.com>
2022-07-11 11:01 ` [PATCH for-next 3/4] io_uring: grow a field in struct io_uring_cmd Kanchan Joshi
2022-07-11 17:00 ` Sagi Grimberg
2022-07-11 17:19 ` Jens Axboe
2022-07-11 17:18 ` Jens Axboe
2022-07-11 17:55 ` Sagi Grimberg
2022-07-11 18:22 ` Sagi Grimberg
2022-07-11 18:24 ` Jens Axboe
2022-07-11 18:58 ` Sagi Grimberg
2022-07-12 11:40 ` Kanchan Joshi
2022-07-14 3:40 ` Ming Lei
2022-07-14 8:19 ` Kanchan Joshi
2022-07-14 15:30 ` Daniel Wagner
2022-07-15 11:07 ` Kanchan Joshi
2022-07-18 9:03 ` Daniel Wagner
[not found] ` <CGME20220711110827epcas5p3fd81f142f55ca3048abc38a9ef0d0089@epcas5p3.samsung.com>
2022-07-11 11:01 ` [PATCH for-next 4/4] nvme-multipath: add multipathing for uring-passthrough commands Kanchan Joshi
2022-07-11 13:51 ` Sagi Grimberg
2022-07-11 15:12 ` Stefan Metzmacher
2022-07-11 16:58 ` Sagi Grimberg
2022-07-11 18:54 ` Kanchan Joshi
2022-07-11 18:37 ` Kanchan Joshi
2022-07-11 19:56 ` Sagi Grimberg
2022-07-12 4:23 ` Kanchan Joshi
2022-07-12 21:26 ` Sagi Grimberg
2022-07-13 5:37 ` Kanchan Joshi
2022-07-13 9:03 ` Sagi Grimberg
2022-07-13 11:28 ` Kanchan Joshi
2022-07-13 12:17 ` Sagi Grimberg
2022-07-14 15:14 ` Ming Lei
2022-07-14 23:05 ` Kanchan Joshi
2022-07-15 1:35 ` Ming Lei
2022-07-15 1:46 ` Ming Lei
2022-07-15 4:24 ` Kanchan Joshi
2022-07-12 6:52 ` Christoph Hellwig
2022-07-12 11:33 ` Kanchan Joshi
2022-07-12 20:13 ` Sagi Grimberg
2022-07-13 5:36 ` Christoph Hellwig
2022-07-13 8:04 ` Sagi Grimberg [this message]
2022-07-13 10:12 ` Christoph Hellwig
2022-07-13 11:00 ` Sagi Grimberg
2022-07-13 11:28 ` Christoph Hellwig
2022-07-13 12:16 ` Sagi Grimberg
2022-07-13 11:49 ` Hannes Reinecke
2022-07-13 12:43 ` Sagi Grimberg
2022-07-13 13:30 ` Hannes Reinecke
2022-07-13 13:41 ` Sagi Grimberg
2022-07-13 14:07 ` Hannes Reinecke
2022-07-13 15:59 ` Sagi Grimberg
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