Re: [dpdk-dev] [RFC PATCH v3 2/3] eal: add mask and unmask interrupt APIs

["Hyong Youb Kim (hyonkim)" <hyonkim@cisco.com>]

> -----Original Message-----
> From: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
> Sent: Wednesday, July 17, 2019 3:15 PM
> To: Hyong Youb Kim (hyonkim) <hyonkim@cisco.com>; Nithin Kumar
> Dabilpuram <ndabilpuram@marvell.com>; David Marchand
> <david.marchand@redhat.com>; Thomas Monjalon
> <thomas@monjalon.net>; Ferruh Yigit <ferruh.yigit@intel.com>; Bruce
> Richardson <bruce.richardson@intel.com>
> Cc: John Daley (johndale) <johndale@cisco.com>; Shahed Shaikh
> <shshaikh@marvell.com>; dev@dpdk.org
> Subject: RE: [RFC PATCH v3 2/3] eal: add mask and unmask interrupt APIs
> 
> > -----Original Message-----
> > From: Hyong Youb Kim (hyonkim) <hyonkim@cisco.com>
> > Sent: Wednesday, July 17, 2019 11:26 AM
> > To: Nithin Kumar Dabilpuram <ndabilpuram@marvell.com>; David
> Marchand
> > <david.marchand@redhat.com>; Thomas Monjalon
> > <thomas@monjalon.net>; Ferruh Yigit <ferruh.yigit@intel.com>; Bruce
> > Richardson <bruce.richardson@intel.com>
> > Cc: Jerin Jacob Kollanukkaran <jerinj@marvell.com>; John Daley (johndale)
> > <johndale@cisco.com>; Shahed Shaikh <shshaikh@marvell.com>;
> > dev@dpdk.org
> > Subject: RE: [RFC PATCH v3 2/3] eal: add mask and unmask interrupt APIs
> > > +rte_intr_mask(const struct rte_intr_handle *intr_handle) {
> > > +	if (intr_handle && intr_handle->type == RTE_INTR_HANDLE_VDEV)
> > > +		return 0;
> > > +
> > > +	if (!intr_handle || intr_handle->fd < 0 || intr_handle->uio_cfg_fd <
> > 0)
> > > +		return -1;
> > > +
> > > +	switch (intr_handle->type){
> > > +	/* Both masking and disabling are same for UIO */
> > > +	case RTE_INTR_HANDLE_UIO:
> > > +		if (uio_intr_disable(intr_handle))
> > > +			return -1;
> > > +		break;
> > > +	case RTE_INTR_HANDLE_UIO_INTX:
> > > +		if (uio_intx_intr_disable(intr_handle))
> > > +			return -1;
> > > +		break;
> > > +	/* not used at this moment */
> > > +	case RTE_INTR_HANDLE_ALARM:
> > > +		return -1;
> > > +#ifdef VFIO_PRESENT
> > > +	case RTE_INTR_HANDLE_VFIO_MSIX:
> > > +	case RTE_INTR_HANDLE_VFIO_MSI:
> > > +		return 0;
> >
> > Isn't this a little confusing? It returns success, but irq is not masked.
> 
> Yes. How about changing the API to rte_intr_ack()(Acknowledge the
> interrupt)
> Or something similar? i.e replace rte_intr_unmask() with rte_intr_ack() for
> this use
> case.
> 

Not sure. I do not have a good suggestion here :-) Like to hear from
David when he comes back, as he spent most time on this issue..

Why not return -1 and let the caller deal with it?

Optimist view:
Maintainers will see the error as vfio-pci + MSI/MSI_X is on
everyone's test list. And it forces them to confront the issue. Do I
really need unmask here, etc.

Pessimist view:
Wastes a lot of people's time. Potentially duplicate code like this
everywhere.

  if (INTx) unmask();

BTW, are you targeting 19.08 or 19.11? Not sure how much change we can
tolerate in 19.08.

Requirements for 19.08 seem to be...
- Must fix the redhat bz (lost interrupt issue with qede + MSI/MSI-X)
- Fix potentially similar issues in other drivers too?

Thanks..
-Hyong

> > As is, return code 0 means...
> > - igb_uio: irq is masked for INTx, MSI, MSI-X
> > - vfio-pci + INTx: irq is masked
> > - vfio-pci + MSI/MSI-X: no changes
> >
> > Masking is useful only for INTx, IMO...
> >
> > Masking MSI/MSI-X via PCI-defined mechanisms (e.g. Mask bit in MSI-X
> > Table) has no practical use for drivers. Handshaking/masking/unmasking is
> > done via device/vendor specific ways, as needed. See all those
> > ack/block/unblock/credit/... mechanisms used in various drivers/NICs to
> > control interrupts their own way.
> >
> > A long time ago in early PCIe days, the linux kernel did auto-masking for
> > MSI/MSI-X (i.e. mask before calling netdev irq handler). It was soon
> removed
> > as it was unnecessary overhead (expensive PIOs to NIC for every interrupt).
> > Windows and FreeBSD do not do auto-masking either.
> 
> rte_intr_ack() can abstract FreeBSD and Windows difference.
>