Re: [PATCH 2/4] nvme/pci: Mask legacy and MSI in threaded handler

[Ming Lei <ming.lei@redhat.com>]

On Thu, Nov 28, 2019 at 02:58:22AM +0900, Keith Busch wrote:
> Local interrupts are re-enabled when the nvme irq thread is
> woken. Subsequent MSI or a level triggered legacy interrupts may restart
> the nvme irq check while the thread handler is running. This unnecessarily
> spends CPU cycles and potentially triggers spurious interrupt detection,
> disabling our NVMe irq.
> 
> Use the NVMe interrupt mask/clear registers to disable controller
> interrupts while the nvme bottom half processes completions.
> 
> Signed-off-by: Keith Busch <kbusch@kernel.org>
> ---
>  drivers/nvme/host/pci.c | 27 +++++++++++++++++++++++++++
>  1 file changed, 27 insertions(+)
> 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 9d307593b94f..c5b837cba730 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -1048,6 +1048,28 @@ static irqreturn_t nvme_irq_check(int irq, void *data)
>  	return IRQ_NONE;
>  }
>  
> +static irqreturn_t nvme_irq_thread_msi(int irq, void *data)
> +{
> +	struct nvme_queue *nvmeq = data;
> +	struct nvme_dev *dev = nvmeq->dev;
> +
> +	nvme_irq(irq, data);
> +	writel(1 << nvmeq->cq_vector, dev->bar + NVME_REG_INTMC);
> +	return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t nvme_irq_check_msi(int irq, void *data)
> +{
> +	struct nvme_queue *nvmeq = data;
> +	struct nvme_dev *dev = nvmeq->dev;
> +
> +	if (nvme_cqe_pending(nvmeq)) {
> +		writel(1 << nvmeq->cq_vector, dev->bar + NVME_REG_INTMS);
> +		return IRQ_WAKE_THREAD;
> +	}
> +	return IRQ_NONE;
> +}
> +
>  /*
>   * Poll for completions any queue, including those not dedicated to polling.
>   * Can be called from any context.
> @@ -1502,6 +1524,11 @@ static int queue_request_irq(struct nvme_queue *nvmeq)
>  	int nr = nvmeq->dev->ctrl.instance;
>  
>  	if (use_threaded_interrupts) {
> +		/* MSI and Legacy use the same NVMe IRQ masking */
> +		if (!pdev->msix_enabled)
> +			return pci_request_irq(pdev, nvmeq->cq_vector,
> +				nvme_irq_check_msi, nvme_irq_thread_msi,
> +				nvmeq, "nvme%dq%d", nr, nvmeq->qid);
>  		return pci_request_irq(pdev, nvmeq->cq_vector, nvme_irq_check,
>  				nvme_irq, nvmeq, "nvme%dq%d", nr, nvmeq->qid);

Just wondering why don't do that for misx_enabled, and according to
document of request_threaded_irq(), the handler is supposed to
disable the device's interrupt:

 *      If you want to set up a threaded irq handler for your device
 *      then you need to supply @handler and @thread_fn. @handler is
 *      still called in hard interrupt context and has to check
 *      whether the interrupt originates from the device. If yes it
 *      needs to disable the interrupt on the device and return
 *      IRQ_WAKE_THREAD which will wake up the handler thread and run
 *      @thread_fn. This split handler design is necessary to support
 *      shared interrupts.

However, MSI irq controller is said to be one shot safe, see
923aa4c378f9("PCI/MSI: Set IRQCHIP_ONESHOT_SAFE for PCI-MSI irqchips"),
then the question is that if interrupt mask is needed.


Thanks,
Ming


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