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From: Yunhong Jiang <yunhong.jiang@linux.intel.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/5] Threaded MSI interrupt for VFIO PCI device
Date: Tue, 5 Jan 2016 23:42:07 -0800	[thread overview]
Message-ID: <20160106074207.GB15116@jnakajim-build> (raw)
In-Reply-To: <5671DDC0.6040507@redhat.com>

On Wed, Dec 16, 2015 at 10:55:12PM +0100, Paolo Bonzini wrote:
> 
> 
> On 16/12/2015 20:15, Alex Williamson wrote:
> > The consumers would be, for instance, Intel PI + the threaded handler
> > added in this series.  These run independently, the PI bypass simply
> > makes the interrupt disappear from the host when it catches it, but if
> > the vCPU isn't running in the right place at the time of the interrupt,
> > it gets delivered to the host, in which case the secondary consumer
> > implementing handle_irq() provides a lower latency injection than the
> > eventfd path.  If PI isn't supported, only this latter consumer is
> > registered.
> 
> I would implement the two in a single consumer, knowing that only one of
> the two parts would effectively run.  But because of the possibility of
> multiple consumers implementing handle_irq(), I am not sure if this is
> feasible.

So is it possible that we limit only one consumer with handle_irq(), as my 
previous response to Alex? We can extend it in future if we do need support 
multiple consumder implementing handle_irq()?

Thanks
--jyh

> 
> > On the surface it seems like a reasonable solution, though having
> > multiple consumers implementing handle_irq() seems problematic.  Do we
> > get multiple injections if we call them all?
> 
> Indeed.
> 
> > Should we have some way
> > to prioritize one handler versus another?  Perhaps KVM should have a
> > single unified consumer that can provide that sort of logic, though we
> > still need the srcu code added here to protect against registration and
> > irq_handler() races.  Thanks,
> 
> I'm happy to see that we have the same doubts. :)
> 
> Paolo
> --
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  reply	other threads:[~2016-01-06  7:45 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-03 18:22 [PATCH 0/5] Threaded MSI interrupt for VFIO PCI device Yunhong Jiang
2015-12-03 18:22 ` [PATCH 1/5] KVM: Extract the irqfd_wakeup_pollin/irqfd_wakeup_pollup Yunhong Jiang
2015-12-03 18:22 ` [PATCH 2/5] VIRT: Support runtime irq_bypass consumer Yunhong Jiang
2015-12-16 19:48   ` Alex Williamson
2015-12-03 18:22 ` [PATCH 3/5] VFIO: Support threaded interrupt handling on VFIO Yunhong Jiang
2015-12-16 19:49   ` Alex Williamson
2015-12-03 18:22 ` [PATCH 4/5] KVM: Add the irq handling consumer Yunhong Jiang
2015-12-04  0:33   ` kbuild test robot
2015-12-03 18:22 ` [PATCH 5/5] KVM: Expose x86 kvm_arch_set_irq_inatomic() Yunhong Jiang
2015-12-03 18:55 ` [PATCH 0/5] Threaded MSI interrupt for VFIO PCI device Alex Williamson
2015-12-03 22:31   ` Yunhong Jiang
2015-12-16 17:56 ` Paolo Bonzini
2015-12-16 19:15   ` Alex Williamson
2015-12-16 21:55     ` Paolo Bonzini
2016-01-06  7:42       ` Yunhong Jiang [this message]
2016-01-06  7:40     ` Yunhong Jiang

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