Re: [PATCH] nvme: reserve a keep-alive admin tag for all transports

[Chao S]

On Fri, May 8, 2026, Christoph Hellwig wrote:
> 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.

Thanks for recalling the working-group history and the spec citation - both
will appear in the v2 commit message.  "PCIe MAY support KATO,
not required" will be the foundation for v2's frame.

Chao


On Fri, May 8, 2026 at 5:04 AM Christoph Hellwig <hch@xxxxxx> wrote:
>
> 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.