netdev - Re: [PATCH net-next v2 0/8] ice: support dynamic interrupt allocation

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Date:   Wed, 22 Mar 2023 10:33:31 -0700
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     Piotr Raczynski <piotr.raczynski@...el.com>,
        <intel-wired-lan@...ts.osuosl.org>
CC:     <netdev@...r.kernel.org>, <michal.swiatkowski@...el.com>,
        <shiraz.saleem@...el.com>, <sridhar.samudrala@...el.com>,
        <jesse.brandeburg@...el.com>, <aleksander.lobakin@...el.com>,
        <lukasz.czapnik@...el.com>
Subject: Re: [PATCH net-next v2 0/8] ice: support dynamic interrupt allocation



On 3/22/2023 9:25 AM, Piotr Raczynski wrote:
> This patchset reimplements MSIX interrupt allocation logic to allow dynamic
> interrupt allocation after MSIX has been initially enabled. This allows
> current and future features to allocate and free interrupts as needed and
> will help to drastically decrease number of initially preallocated
> interrupts (even down to the API hard limit of 1). Although this patchset
> does not change behavior in terms of actual number of allocated interrupts
> during probe, it will be subject to change.
> 
> First few patches prepares to introduce dynamic allocation by moving
> interrupt allocation code to separate file and update allocation API used
> in the driver to the currently preferred one.
> 
> Due to the current contract between ice and irdma driver which is directly
> accessing msix entries allocated by ice driver, even after moving away from
> older pci_enable_msix_range function, still keep msix_entries array for
> irdma use.
> 
> Next patches refactors and removes redundant code from SRIOV related logic
> as it also make it easier to move away from static allocation scheme.
> 
> Last patches actually enables dynamic allocation of MSIX interrupts. First,
> introduce functions to allocate and free interrupts individually. This sets
> ground for the rest of the changes even if that patch still allocates the
> interrupts from the preallocated pool. Since this patch starts to keep
> interrupt details in ice_q_vector structure we can get rid of functions
> that calculates base vector number and register offset for the interrupt
> as it is equal to the interrupt index. Only keep separate register offset
> functions for the VF VSIs.
> 
> Next, replace homegrown interrupt tracker with much simpler xarray based
> approach. As new API always allocate interrupts one by one, also track
> interrupts in the same manner.
> 
> Lastly, extend the interrupt tracker to deal both with preallocated and
> dynamically allocated vectors and use pci_msix_alloc_irq_at and
> pci_msix_free_irq functions. Since not all architecture supports dynamic
> allocation, check it before trying to allocate a new interrupt.
> 
> As previously mentioned, this patchset does not change number of initially
> allocated interrupts during init phase but now it can and will likely be
> changed.
> 
> Patch 1-3 -> move code around and use newer API
> Patch 4-5 -> refactor and remove redundant SRIOV code
> Patch 6   -> allocate every interrupt individually
> Patch 7   -> replace homegrown interrupt tracker with xarray
> Patch 8   -> allow dynamic interrupt allocation
> 
> Change history:
> v1 -> v2:
> - ice: refactor VF control VSI interrupt handling
>   - move ice_get_vf_ctrl_vsi to ice_lib.c (ice_vf_lib.c depends on
>     CONFIG_PCI_IOV)
> 

The other option would have been to make ice_vf_lib.h have a no-op
function that always returned NULL, since we generally would know that
there are no VF ctrl VSI if CONFIG_PCI_IOV is disabled.

But I'm ok with it being in ice_lib.c too.

Thanks,
Jake