linux-kernel - Re: A question about NVMe's nvme-irq

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Date:	Fri, 21 Mar 2014 16:11:09 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	liaohengquan1986 <liaohengquan1986@....com>
Cc:	"Alexander Gordeev" <agordeev@...hat.com>,
	linux-kernel@...r.kernel.org,
	"Keith Busch" <keith.busch@...el.com>,
	linux-nvme@...ts.infradead.org
Subject: Re: A question about NVMe's nvme-irq

On Fri, Mar 21, 2014 at 11:29:02AM +0800, liaohengquan1986 wrote:
> hello,
>          There is question confusing me recently. In the function of nvme-irq as belows:
>           static irqreturn_t nvme_irq(int irq, void *data)
>           {
>                  irqreturn_t result;
>                  struct nvme_queue *nvmeq = data;
>                  spin_lock(&nvmeq->q_lock);
>                  nvme_process_cq(nvmeq);
>                  result = nvmeq->cqe_seen ? IRQ_HANDLED : IRQ_NONE;
>                  nvmeq->cqe_seen = 0;
>                  spin_unlock(&nvmeq->q_lock);
>                  return result;
>        }
>        If there are two cqes which trigger two irqs, but they are so closed that the first nvme-irq() handles both the cqes( including the second cqe which triggers the second irq),
>       then the second nvme_process_cq() will find there is no cqe in the CQ and return nvmeq->cqe_seen = 0, and nvme-irq will return IRQ_NONE.
>       I think maybe this is a bug, because there actually are two irqs, it's not right to return IRQ_NONE, isn't it?

        /* If the controller ignores the cq head doorbell and continuously
         * writes to the queue, it is theoretically possible to wrap around
         * the queue twice and mistakenly return IRQ_NONE.  Linux only
         * requires that 0.1% of your interrupts are handled, so this isn't
         * a big problem.
         */

I should probably update & move that comment, but nevertheless, it
applies to your situation too.

> 
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