linux-kernel - Re: [PATCH 0/5] Threaded MSI interrupt for VFIO PCI device

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Date:	Wed, 16 Dec 2015 18:56:45 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Yunhong Jiang <yunhong.jiang@...ux.intel.com>,
	alex.williamson@...hat.com
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/5] Threaded MSI interrupt for VFIO PCI device

Alex,

can you take a look at the extension to the irq bypass interface in
patch 2?  I'm not sure I understand what is the case where you have
multiple consumers for the same token.

Paolo

On 03/12/2015 19:22, Yunhong Jiang wrote:
> When assigning a VFIO device to a KVM guest with low latency requirement, it  
> is better to handle the interrupt in the hard interrupt context, to reduce 
> the context switch to/from the IRQ thread.
> 
> Based on discussion on https://lkml.org/lkml/2015/10/26/764, the VFIO msi 
> interrupt is changed to use request_threaded_irq(). The primary interrupt 
> handler tries to set the guest interrupt atomically. If it fails to achieve 
> it, a threaded interrupt handler will be invoked.
> 
> The irq_bypass manager is extended for this purpose. The KVM eventfd will 
> provide a irqbypass consumer to handle the interrupt at hard interrupt 
> context. The producer will invoke the consumer's handler then.
> 
> Yunhong Jiang (5):
>   Extract the irqfd_wakeup_pollin/irqfd_wakeup_pollup
>   Support runtime irq_bypass consumer
>   Support threaded interrupt handling on VFIO
>   Add the irq handling consumer
>   Expose x86 kvm_arch_set_irq_inatomic()
> 
>  arch/x86/kvm/Kconfig              |   1 +
>  drivers/vfio/pci/vfio_pci_intrs.c |  39 ++++++++++--
>  include/linux/irqbypass.h         |   8 +++
>  include/linux/kvm_host.h          |  19 +++++-
>  include/linux/kvm_irqfd.h         |   1 +
>  virt/kvm/Kconfig                  |   3 +
>  virt/kvm/eventfd.c                | 131 ++++++++++++++++++++++++++------------
>  virt/lib/irqbypass.c              |  82 ++++++++++++++++++------
>  8 files changed, 214 insertions(+), 70 deletions(-)
> 
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