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

[Jerin Jacob Kollanukkaran <jerinj@marvell.com>]

> -----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.
 
> 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.