Re: [dpdk-dev] [PATCH 1/2] eal: make max interrupt vector id configurable

[David Marchand <david.marchand@redhat.com>]

On Wed, Mar 24, 2021 at 1:55 PM Jerin Jacob <jerinjacobk@gmail.com> wrote:
> > > IMO, We dont need to make it configurable and each platform sets its
> > > value. That scheme won't work as generic distribution build will fail
> > > to run.
> > > Since PCIe specification defines this value and there is no
> > > performance impact on increasing this,
> > > IMO, We can change to 2048 as default.
> >
> > It probably breaks rte_intr_* ABI.
>
> Yes. Even though all APIs are used as a pointer (ie. "struct
> rte_intr_handle *"), the definition
> kept in the header file.
>
>
> > struct rte_intr_handle {
> > ...
> >         int efds[RTE_MAX_RXTX_INTR_VEC_ID];  /**< intr vectors/efds mapping */
> >         struct rte_epoll_event elist[RTE_MAX_RXTX_INTR_VEC_ID];
> >                                        /**< intr vector epoll event */
> > ...
> >
> >
> > I see you need this for octeontx2, so wondering if you could handle
> > this differently in octeontx2 drivers?
>
> This is an issue with any PCIe device that has more than 512 MSIX interrupts.
>
> The PCI spec the max is defined as 2K.
>
> CN10K drivers have 1K interrupt lines per PCIe device.
>
> I think, following are the options.
> 1) To avoid ABI breakage  in default configuration use the existing patch
> 2) In 21.11 break ABI and Either change to
> a) RTE_MAX_RXTX_INTR_VEC_ID as 1024
> or
> b) Make it full dynamic allocation based on PCI device MSIX size on probe time.
> That brings some kind of dependency rte_intr with PCI device. Need to
> understand,
> How it can clearly be abstracted out and Is it worth trouble for the
> amount of memory.
> Looks like the cost of one entry is 40B. So additional 512 is 40B *
> 512 =  21KB virtual memory.

Since you mentioned performance is not impacted, I guess this is
control path only.
And there is no need to expose this.
So:

c) Rework API so that we don't expose such details.


-- 
David Marchand