Re: [PATCH 4/4] nvme/pci: Spin threaded interrupt completions

From: Sagi Grimberg <sagi@grimberg.me>
To: Keith Busch <kbusch@kernel.org>,
	linux-nvme@lists.infradead.org, hch@lst.de
Cc: bigeasy@linutronix.de, helgaas@kernel.org, ming.lei@redhat.com
Subject: Re: [PATCH 4/4] nvme/pci: Spin threaded interrupt completions
Date: Wed, 27 Nov 2019 18:46:55 -0800	[thread overview]
Message-ID: <11325d8e-e9f8-408e-18c3-182c69e90eab@grimberg.me> (raw)
In-Reply-To: <20191127175824.1929-5-kbusch@kernel.org>

> For deeply queued workloads, the nvme controller may be posting
> new completions while the threaded interrupt handles previous
> completions. Since the interrupts are masked, we can spin for these
> completions for as long as new completions are being posted.
> 
> Signed-off-by: Keith Busch <kbusch@kernel.org>
> ---
>   drivers/nvme/host/pci.c | 10 ++++++++--
>   1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 571b33b69c5f..9ec0933eb120 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -1042,9 +1042,15 @@ static irqreturn_t nvme_irq(int irq, void *data)
>   	return ret;
>   }
>   
> +static void nvme_irq_spin(int irq, void *data)
> +{
> +	while (nvme_irq(irq, data) != IRQ_NONE)
> +		cond_resched();

So the cond_resched should be fair to multiple devices mapped to the
same cpu core I assume.. did you happen to test it?

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