From: "Michael S. Tsirkin" <mst@redhat.com>
To: Avi Kivity <avi@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
Sheng Yang <sheng@linux.intel.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
kvm@vger.kernel.org
Subject: Re: [PATCH 0/8][v2] MSI-X mask emulation support for assigned device
Date: Wed, 20 Oct 2010 17:59:44 +0200 [thread overview]
Message-ID: <20101020155944.GA23185@redhat.com> (raw)
In-Reply-To: <4CBF10AC.30309@redhat.com>
On Wed, Oct 20, 2010 at 05:54:20PM +0200, Avi Kivity wrote:
> On 10/20/2010 05:38 PM, Alex Williamson wrote:
> >> > We'll need to optimize interrupt injection and eoi via KVM,
> >> > but it should only be a performance optimization, not a functional
> >> > requirement.
> >>
> >> For level-triggered interrupts only, yes? MSI EOI does not involve any
> >> device or interrupt controller visible action?
> >
> >Right, the EOI is for legacy interrupts only. Perhaps we don't care
> >enough about performance of those to route it through KVM so long as we
> >can co-exist with the KVM APIC.
>
> We will need a way to get the EOI out to userspace, then.
>
> Perhaps that will give us motivation to split the ioapic from the
> kernel (though I suppose fear of regressions will stop us).
>
> Anyway EOI notifiers are also useful for timekeeping.
>
> > MSIs are currently still bouncing from
> >VFIO to QEMU to the guest, which seems inefficient.
>
> Why is that? Can't you use irqfd like vhost-net?
>
> >> > It would probably make sense to request a mask/unmask ioctl in VFIO for
> >> > MSI-X, then perhaps the pending bits would only support read/write (no
> >> > mmap), so we could avoid an ioctl there.
> >>
> >> I would much like to see in-band information (which mask/unmask is for
> >> older Linux) done via eventfds so userspace is not involved.
> >
> >Hmm, I'm not sure how to do that yet.
>
> One ugly way is to use two eventfds, one counting mask events, one
> counting unmask events. The difference is the value if the masked
> bit.
>
> Another option is to use
> http://permalink.gmane.org/gmane.linux.kernel.commits.head/188038
> which allows kvm to maintain a counter using eventfd. The vfio
> state machine then looks like:
>
> interrupt:
> if counter == 0 mask interrupts, set pending bit, wait for counter
> to become 1
> if counter == 1 forward it
> counter becomes 1: unmask, forward interrupt if pending
One issue is that this page has a ton of other info.
KVM would have to keep all that in kernel...
--
MST
next prev parent reply other threads:[~2010-10-20 16:06 UTC|newest]
Thread overview: 66+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-20 8:26 [PATCH 0/8][v2] MSI-X mask emulation support for assigned device Sheng Yang
2010-10-20 8:26 ` [PATCH 1/8] PCI: MSI: Move MSI-X entry definition to pci_regs.h Sheng Yang
2010-10-20 11:07 ` Matthew Wilcox
2010-10-20 8:26 ` [PATCH 2/8] irq: Export irq_to_desc() to modules Sheng Yang
2010-10-20 8:26 ` [PATCH 3/8] KVM: x86: Enable ENABLE_CAP capability for x86 Sheng Yang
2010-10-20 8:26 ` [PATCH 4/8] KVM: Move struct kvm_io_device to kvm_host.h Sheng Yang
2010-10-20 8:26 ` [PATCH 5/8] KVM: Add kvm_get_irq_routing_entry() func Sheng Yang
2010-10-20 8:53 ` Avi Kivity
2010-10-20 8:58 ` Sheng Yang
2010-10-20 9:13 ` Sheng Yang
2010-10-20 9:17 ` Sheng Yang
2010-10-20 9:32 ` Avi Kivity
2010-10-20 8:26 ` [PATCH 6/8] KVM: assigned dev: Preparation for mask support in userspace Sheng Yang
2010-10-20 9:30 ` Avi Kivity
2010-10-22 14:53 ` Marcelo Tosatti
2010-10-24 12:19 ` Sheng Yang
2010-10-24 12:23 ` Michael S. Tsirkin
2010-10-28 8:21 ` Sheng Yang
2010-10-20 8:26 ` [PATCH 7/8] KVM: assigned dev: Introduce io_device for MSI-X MMIO accessing Sheng Yang
2010-10-20 9:46 ` Avi Kivity
2010-10-20 10:33 ` Michael S. Tsirkin
2010-10-21 6:46 ` Sheng Yang
2010-10-21 9:27 ` Avi Kivity
2010-10-21 9:24 ` Michael S. Tsirkin
2010-10-21 9:47 ` Avi Kivity
2010-10-21 10:51 ` Michael S. Tsirkin
2010-10-20 22:35 ` Michael S. Tsirkin
2010-10-21 7:44 ` Sheng Yang
2010-10-20 8:26 ` [PATCH 8/8] KVM: Emulation MSI-X mask bits for assigned devices Sheng Yang
2010-10-20 9:49 ` Avi Kivity
2010-10-20 22:24 ` Michael S. Tsirkin
2010-10-21 8:30 ` Sheng Yang
2010-10-21 8:39 ` Michael S. Tsirkin
2010-10-22 4:42 ` Sheng Yang
2010-10-22 10:17 ` Michael S. Tsirkin
2010-10-22 13:30 ` Sheng Yang
2010-10-22 14:32 ` Michael S. Tsirkin
2010-10-20 9:51 ` [PATCH 0/8][v2] MSI-X mask emulation support for assigned device Avi Kivity
2010-10-20 10:44 ` Michael S. Tsirkin
2010-10-20 10:59 ` Avi Kivity
2010-10-20 13:43 ` Michael S. Tsirkin
2010-10-20 14:58 ` Alex Williamson
2010-10-20 14:58 ` Michael S. Tsirkin
2010-10-20 15:12 ` Alex Williamson
2010-10-20 15:17 ` Avi Kivity
2010-10-20 15:22 ` Alex Williamson
2010-10-20 15:26 ` Avi Kivity
2010-10-20 15:38 ` Alex Williamson
2010-10-20 14:47 ` Alex Williamson
2010-10-20 14:46 ` Michael S. Tsirkin
2010-10-20 15:07 ` Alex Williamson
2010-10-20 15:13 ` Michael S. Tsirkin
2010-10-20 20:13 ` Alex Williamson
2010-10-20 22:06 ` Michael S. Tsirkin
2010-10-20 15:23 ` Avi Kivity
2010-10-20 15:38 ` Alex Williamson
2010-10-20 15:54 ` Avi Kivity
2010-10-20 15:59 ` Michael S. Tsirkin [this message]
2010-10-20 16:13 ` Avi Kivity
2010-10-20 17:11 ` Michael S. Tsirkin
2010-10-20 18:31 ` Alex Williamson
2010-10-21 7:41 ` Sheng Yang
2010-10-20 19:02 ` Marcelo Tosatti
2010-10-21 7:10 ` Sheng Yang
2010-10-21 8:21 ` Michael S. Tsirkin
2010-10-20 22:20 ` Michael S. Tsirkin
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