linux-kernel - Re: [PATCH 3/5] VFIO: Support threaded interrupt handling on VFIO

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Date:	Wed, 16 Dec 2015 12:49:06 -0700
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Yunhong Jiang <yunhong.jiang@...ux.intel.com>, pbonzini@...hat.com
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] VFIO: Support threaded interrupt handling on VFIO

On Thu, 2015-12-03 at 10:22 -0800, Yunhong Jiang wrote:
> For VFIO device with MSI interrupt type, it's possible to handle the
> interrupt on hard interrupt context without invoking the interrupt
> thread. Handling the interrupt on hard interrupt context reduce the
> interrupt latency.
> 
> Signed-off-by: Yunhong Jiang <yunhong.jiang@...ux.intel.com>
> ---
>  drivers/vfio/pci/vfio_pci_intrs.c | 39 ++++++++++++++++++++++++++++++++++-----
>  1 file changed, 34 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/vfio/pci/vfio_pci_intrs.c b/drivers/vfio/pci/vfio_pci_intrs.c
> index 3b3ba15558b7..108d335c5656 100644
> --- a/drivers/vfio/pci/vfio_pci_intrs.c
> +++ b/drivers/vfio/pci/vfio_pci_intrs.c
> @@ -236,12 +236,35 @@ static void vfio_intx_disable(struct vfio_pci_device *vdev)
>  	kfree(vdev->ctx);
>  }
>  
> +static irqreturn_t vfio_msihandler(int irq, void *arg)
> +{
> +	struct vfio_pci_irq_ctx *ctx = arg;
> +	struct irq_bypass_producer *producer = &ctx->producer;
> +	struct irq_bypass_consumer *consumer;
> +	int ret = IRQ_HANDLED, idx;
> +
> +	idx = srcu_read_lock(&producer->srcu);
> +
> +	list_for_each_entry_rcu(consumer, &producer->consumers, sibling) {
> +		/*
> +		 * Invoke the thread handler if any consumer would block, but
> +		 * finish all consumes.
> +		 */
> +		if (consumer->handle_irq(consumer->irq_context) == -EWOULDBLOCK)
> +			ret = IRQ_WAKE_THREAD;
> +		continue;
> +	}
> +
> +	srcu_read_unlock(&producer->srcu, idx);


There should be an irq bypass manager interface to abstract this.
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