From: "Michael S. Tsirkin" <mst@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
gleb@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd
Date: Wed, 5 Sep 2012 18:15:23 +0300 [thread overview]
Message-ID: <20120905151523.GD11058@redhat.com> (raw)
In-Reply-To: <50476BC4.4050807@redhat.com>
On Wed, Sep 05, 2012 at 06:12:04PM +0300, Avi Kivity wrote:
> On 09/05/2012 06:09 PM, Michael S. Tsirkin wrote:
> > On Wed, Sep 05, 2012 at 05:51:53PM +0300, Michael S. Tsirkin wrote:
> >> On Wed, Sep 05, 2012 at 05:35:43PM +0300, Avi Kivity wrote:
> >> > On 08/22/2012 03:41 AM, Michael S. Tsirkin wrote:
> >> > >>
> >> > >> I assumed you were pointing out the level vs edge interaction. If we
> >> > >> call that a userspace bug, I can just drop this. Thanks,
> >> > >>
> >> > >> Alex
> >> > >
> >> > > level is userspace bug I think :)
> >> >
> >> > I don't see how it's a bug. Suppose we have a vfio device that shares a
> >> > gsi with an emulated device. The emulated device naturally uses
> >> > KVM_IRQ_LINE (it has no need to re-sample on ADN), while vfio naturally
> >> > has to use irqfd.
> >>
> >> Absolutely. But vfio needs to use irqfd with the new flag.
> >> Using existing irqfd for level is a bug.
> >>
> >> > Note one would expect that each irqfd gets its own irq source id, since
> >> > they are all independent level sources. The reason they don't is that
> >> > we shut them down anyway and let the sources re-trigger (it is more
> >> > accurate to say that they have no irq source id, but that would just
> >> > muddle the implementation).
> >> >
> >> > Alex, if the conclusion is that we do need this patch, then please add a
> >> > comment explaining why we can share the source id among all irqfd users.
> >
> > Something along the lines of
> >
> > /*
> > For resample irqfds, level is a logical OR of all inputs;
> > to support this, track state for RESAMPLE irqfds separately
> > from userspace. We do not need to track state for each input since
> > they are all deasserted at the same time, before resampling.
> > */
>
> Well the comment style is wrong.
Ouch.
> To expand a little more, irqfd only sends assert events, so assigning
> the level is equivalent to an OR. Clearing an resampling simply builds
> the state again.
>
> btw, there can be other irq source IDs if the lines are shared with the
> PIT or kvm assigned devices.
Nod.
> --
> error compiling committee.c: too many arguments to function
next prev parent reply other threads:[~2012-09-05 15:14 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-21 19:28 [PATCH v9 0/2] kvm: level irqfd support Alex Williamson
2012-08-21 19:29 ` [PATCH v9 1/2] kvm: Use a reserved IRQ source ID for irqfd Alex Williamson
2012-08-21 19:58 ` Michael S. Tsirkin
2012-08-21 20:06 ` Alex Williamson
2012-08-21 20:41 ` Michael S. Tsirkin
2012-08-21 21:14 ` Alex Williamson
2012-08-22 0:41 ` Michael S. Tsirkin
2012-08-22 1:34 ` Alex Williamson
2012-09-05 14:35 ` Avi Kivity
2012-09-05 14:51 ` Michael S. Tsirkin
2012-09-05 14:59 ` Avi Kivity
2012-09-05 15:13 ` Michael S. Tsirkin
2012-09-05 15:22 ` Avi Kivity
2012-09-05 15:28 ` Michael S. Tsirkin
2012-09-05 15:35 ` Avi Kivity
2012-09-05 15:09 ` Michael S. Tsirkin
2012-09-05 15:12 ` Avi Kivity
2012-09-05 15:15 ` Michael S. Tsirkin [this message]
2012-09-05 14:46 ` Avi Kivity
2012-09-05 15:07 ` Michael S. Tsirkin
2012-09-05 15:15 ` Avi Kivity
2012-08-21 19:29 ` [PATCH v9 2/2] kvm: On Ack, De-assert & Notify KVM_IRQFD extension Alex Williamson
2012-08-21 20:37 ` Michael S. Tsirkin
2012-08-21 21:11 ` Alex Williamson
2012-08-22 0:14 ` Michael S. Tsirkin
2012-08-22 1:48 ` Alex Williamson
2012-09-05 14:57 ` Avi Kivity
2012-09-17 16:13 ` Alex Williamson
2012-08-22 0:31 ` [PATCH v9 0/2] kvm: level irqfd support Michael S. Tsirkin
2012-08-22 1:28 ` Alex Williamson
2012-08-22 8:25 ` Michael S. Tsirkin
2012-09-17 18:08 ` Alex Williamson
2012-08-22 10:10 ` Michael S. Tsirkin
2012-09-05 14:42 ` Avi Kivity
2012-09-05 14:52 ` Michael S. Tsirkin
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