Re: [PATCH 10/15] hw/nvme: Make max_ioqpairs and msix_qsize configurable in runtime

[Klaus Jensen]

On Oct  7 18:24, Lukasz Maniak wrote:
> From: Łukasz Gieryk <lukasz.gieryk@linux.intel.com>
> 
> The Nvme device defines two properties: max_ioqpairs, msix_qsize. Having
> them as constants is problematic for SR-IOV support.
> 
> The SR-IOV feature introduces virtual resources (queues, interrupts)
> that can be assigned to PF and its dependent VFs. Each device, following
> a reset, should work with the configured number of queues. A single
> constant is no longer sufficient to hold the whole state.
> 
> This patch tries to solve the problem by introducing additional
> variables in NvmeCtrl’s state. The variables for, e.g., managing queues
> are therefore organized as:
> 
>  - n->params.max_ioqpairs – no changes, constant set by the user.
> 
>  - n->max_ioqpairs - (new) value derived from n->params.* in realize();
>                      constant through device’s lifetime.
> 
>  - n->(mutable_state) – (not a part of this patch) user-configurable,
>                         specifies number of queues available _after_
>                         reset.
> 
>  - n->conf_ioqpairs - (new) used in all the places instead of the ‘old’
>                       n->params.max_ioqpairs; initialized in realize()
>                       and updated during reset() to reflect user’s
>                       changes to the mutable state.
> 
> Since the number of available i/o queues and interrupts can change in
> runtime, buffers for sq/cqs and the MSIX-related structures are
> allocated big enough to handle the limits, to completely avoid the
> complicated reallocation. A helper function (nvme_update_msixcap_ts)
> updates the corresponding capability register, to signal configuration
> changes.
> 
> Signed-off-by: Łukasz Gieryk <lukasz.gieryk@linux.intel.com>

Instead of this, how about adding new parameters, say, sriov_vi_private
and sriov_vq_private. Then, max_ioqpairs and msix_qsize are still the
"physical" limits and the new parameters just reserve some for the
primary controller, the rest being available for flexsible resources.

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