Messages in this thread Patch in this message | | | From | Andrey Zhizhikin <> | Subject | [PATCH] uio: Allow to take irq bottom-half into irq_handler with additional dt-binding | Date | Wed, 6 Dec 2017 15:55:40 +0100 |
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Certain Kernel preemption models are using threaded interrupt handlers, which is in general quite beneficial. However, threaded handlers introducing additional scheduler overhead, when the bottom-half thread should be woken up and scheduled for execution. This can result is additional latency, which in certain cases is not desired.
UIO driver with Generic IRQ handler, that wraps a HW block might suffer a small degradation when it's bottom half is executed, since it needs its bottom half to be woken up by the scheduler every time INT is delivered. For high rate INT signals, this also bring additional undesired load on the scheduler itself.
Since the actual ACK is performed in the top-half, and bottom-half of the UIO driver with Generic IRQ handler is relatively slick (only flag is set based on the INT reception), it might be beneficial to move this bottom-half to the irq_handler itself, rather than to have a separate thread to service it.
This patch aims to address the task above, and in addition introduces a new dt-binding which could be configured on a per-node basis. That means developers utilizing the UIO driver could decide which UIO instance is critical in terms of interrupt processing, and move their corresponding bottom-halves to the irq_handler to fight additional scheduling latency.
New DT binding: - no-threaded-irq: when present, request_irq() is called with IRQF_NO_THREAD flag set, effectively skipping threaded interrupt handler and taking bottom-half into irq_handler
Signed-off-by: Andrey Zhizhikin <andrey.z@gmail.com>
diff --git a/drivers/uio/uio_pdrv_genirq.c b/drivers/uio/uio_pdrv_genirq.c index f598ecd..86427a4 100644 --- a/drivers/uio/uio_pdrv_genirq.c +++ b/drivers/uio/uio_pdrv_genirq.c @@ -108,6 +108,7 @@ static int uio_pdrv_genirq_probe(struct platform_device *pdev) struct uio_pdrv_genirq_platdata *priv; struct uio_mem *uiomem; int ret = -EINVAL; + int no_threaded_irq = 0; int i; if (pdev->dev.of_node) { @@ -121,6 +122,14 @@ static int uio_pdrv_genirq_probe(struct platform_device *pdev) uioinfo->name = pdev->dev.of_node->name; uioinfo->version = "devicetree"; /* Multiple IRQs are not supported */ + + /* read additional property (if exists) and decide whether + * to have IRQ bottom half to be executed in a separate + * thread, or to have it executed in the irq_handler + * context + */ + if (of_property_read_bool(pdev->dev.of_node, "no-threaded-irq")) + no_threaded_irq = 1; } if (!uioinfo || !uioinfo->name || !uioinfo->version) { @@ -134,6 +143,12 @@ static int uio_pdrv_genirq_probe(struct platform_device *pdev) return ret; } + /* execute BH in irq_handler if property set in FDT */ + if ((no_threaded_irq > 0) && !(uioinfo->irq_flags & IRQF_NO_THREAD)) { + dev_info(&pdev->dev, "promoting INT with IRQF_NO_THREAD\n"); + uioinfo->irq_flags |= IRQF_NO_THREAD; + } + priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL); if (!priv) { dev_err(&pdev->dev, "unable to kmalloc\n"); -- 2.7.4
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