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Date: Fri, 8 May 2026 11:04:27 +0200
From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Maurizio Lombardi <mlombard@arkamax.eu>, Chao Shi <coshi036@gmail.com>,
	linux-nvme@lists.infradead.org, Christoph Hellwig <hch@lst.de>,
	Sagi Grimberg <sagi@grimberg.me>, Jens Axboe <axboe@kernel.dk>,
	Tatsuya Sasaki <tatsuya6.sasaki@kioxia.com>,
	linux-kernel@vger.kernel.org, Sungwoo Kim <iam@sung-woo.kim>,
	Dave Tian <daveti@purdue.edu>, Weidong Zhu <weizhu@fiu.edu>
Subject: Re: [PATCH] nvme: reserve a keep-alive admin tag for all transports
Message-ID: <20260508090427.GA20593@lst.de>
References: <20260428022911.1288485-1-coshi036@gmail.com> <afBYFfZJjiDDvlLv@kbusch-mbp.client.m3-hotspots.de> <DI4LPUI48MRH.3GC5TVZLMICXN@arkamax.eu> <afBgs0f8Et3jqijM@kbusch-mbp.client.m3-hotspots.de>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Apr 28, 2026 at 08:24:35AM +0100, Keith Busch wrote:
> > This field specifies the timeout value for the Keep Alive feature in
> > milliseconds.  [...]
> > The default value for this field is 0h for NVMe transports that do not require use of the Keep Alive
> > feature (e.g., NVMe over PCIe). For NVMe transports that require use of the Keep Alive feature
> > (e.g., RDMA and TCP), the default value for this field is 1D4C0h "
> > 
> > To me, it sounds like for nvme-pci, keep alive isn't required, but could
> > be activated.
> 
> The spec says the support is subject to the Transport binding
> specification, which does not exist in the PCIe transport spec.

My memories from the fabrics working group back in the day is that we
explicitly intended to support it in PCIe.  The wording in the spec
referring to transport specs I can find is:

The NVMe Transport binding specification for the associated NVMe Transport
defines:

 o the minimum Keep Alive Timeout value, if any;
 o the maximum Keep Alive Timeout value, if any; and
 o if the Keep Alive Timer feature is required to be supported and enabled.

which does not read to me like there is any required language in the
transport spec to require keep alive.