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From: "Hyong Youb Kim (hyonkim)" <hyonkim@cisco.com>
To: Jerin Jacob Kollanukkaran <jerinj@marvell.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" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [RFC PATCH v3 2/3] eal: add mask and unmask interrupt APIs
Date: Wed, 17 Jul 2019 09:51:21 +0000	[thread overview]
Message-ID: <MWHPR11MB1839DD52B8EFB3BE383FCFDCBFC90@MWHPR11MB1839.namprd11.prod.outlook.com> (raw)
In-Reply-To: <BYAPR18MB24244A2FD8DA4DFF573C5D20C8C90@BYAPR18MB2424.namprd18.prod.outlook.com>

> -----Original Message-----
> From: Jerin Jacob Kollanukkaran <jerinj@marvell.com>
> Sent: Wednesday, July 17, 2019 6:21 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
> 
> > > > 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..
> > >
> > > Sure. He is on vacation.
> > > Any reason for thinking, rte_intr_ack()  may not be semantically correct?
> > > I think, it is very much correct if there are no better suggestions.
> > > Anyway it the name, From VFIO perspective, we know what is expected
> so
> > > I think it is fine.
> > >
> > > >
> > > > Why not return -1 and let the caller deal with it?
> > >
> > > If we make it as rte_intr_ack() no need to return -1 for
> > > MSIX-VFIO+Linux as it is semantically correct.
> > >
> >
> > Ack can be ambiguous. For INTx, ack usually means PIO to a NIC register,
> > saying "I got your interrupt, please de-assert irq".
> 
> I think, it vary from the perspective of IRQ Chip(or controller) vs NIC
> register(Source) PoV.
> Since the API starts from rte_intr_* it is more of controller so _ack_ make
> sense
> Other reason for ack:
> 1) It will enforce that it needs to be called form ISR
> 2) It would be have been really correct to unmask if VFIO+MSIx+Linux
> supports
> it
> 3) if it is ack, no need to add unmask counterpart, the _mask_ API
> 

Just curious, what you mean by irq controller? Ack/mask/unmask PIOs
all go to the NIC. It is the NIC that asserts/de-asserts irq..

> >
> > Besides the name, are we agreeing that we want these?
> > - Unmask if INTx
> 
> Yes
> 
> > - Nothing if MSI/MSI-X
> Yes for MSI over VFIO
> No for MSI over UIO/igb_uio
> 

I guess I was not clear. For MSI/MSI-X, we do not want to do
mask/unmask regardless of vfio-pci/igb_uio.  Below is my comment about
linux/windows/freebsd from an earlier email. Do you disagree? I am
sure there are plenty of kernel NIC driver guys here. Please correct
me if I am mistaken...

---
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.
---

Most drivers have a single irq callback.

handler() {
  do_action()
  rte_intr_umask/ack()
}

Suppose MSI/MSI-X is used (super likely since it is the default).
With igb_uio, rte_intr_umask/ack() will actually do PIO writes to the
NIC to unmask. This is unnecessary overhead.

> I don't  have very strong opinion unmask vs ack. I prefer to have ack due the
> reasons stated above.
> If you really have strong opinion on using unmask, we will stick with that to
> make forward progress.
> Let us know.
> 

I have no strong opinion either.

Thanks..
-Hyong


  reply	other threads:[~2019-07-17  9:51 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-15 16:50 [dpdk-dev] [RFC PATCH] vfio: avoid re-installing irq handler Jerin Jacob Kollanukkaran
2019-07-16  5:58 ` Hyong Youb Kim (hyonkim)
2019-07-16  6:47   ` Jerin Jacob Kollanukkaran
2019-07-16  7:49     ` Hyong Youb Kim (hyonkim)
2019-07-16  9:56       ` Jerin Jacob Kollanukkaran
2019-07-16  6:46 ` [dpdk-dev] [RFC PATCH] eal: add mask and unmask interrupt apis Nithin Dabilpuram
2019-07-16  7:01 ` [dpdk-dev] [RFC PATCH v2] " Nithin Dabilpuram
2019-07-16 16:44 ` [dpdk-dev] [RFC PATCH v3 1/3] vfio: revert change that does intr eventfd setup at probe Nithin Dabilpuram
2019-07-16 16:44   ` [dpdk-dev] [RFC PATCH v3 2/3] eal: add mask and unmask interrupt APIs Nithin Dabilpuram
2019-07-17  5:55     ` Hyong Youb Kim (hyonkim)
2019-07-17  6:14       ` Jerin Jacob Kollanukkaran
2019-07-17  7:09         ` Hyong Youb Kim (hyonkim)
2019-07-17  8:03           ` Jerin Jacob Kollanukkaran
2019-07-17  8:45             ` Hyong Youb Kim (hyonkim)
2019-07-17  9:20               ` Jerin Jacob Kollanukkaran
2019-07-17  9:51                 ` Hyong Youb Kim (hyonkim) [this message]
2019-07-17 10:43                   ` Jerin Jacob Kollanukkaran
2019-07-17 11:06                     ` Hyong Youb Kim (hyonkim)
2019-07-17 11:16                       ` Jerin Jacob Kollanukkaran
2019-07-17 12:04                         ` Nithin Kumar Dabilpuram
2019-07-16 16:44   ` [dpdk-dev] [RFC PATCH v3 3/3] drivers/net: use unmask API in interrupt handlers Nithin Dabilpuram
2019-07-17  6:01     ` Hyong Youb Kim (hyonkim)
2019-07-17  7:47       ` Nithin Kumar Dabilpuram
2019-07-16 20:06   ` [dpdk-dev] [RFC PATCH v3 1/3] vfio: revert change that does intr eventfd setup at probe Stephen Hemminger

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