[PATCHv3 2/4] nvme/pci: Complete commands from primary handler

[Keith Busch <kbusch@kernel.org>]

The context switch to wake the threaded interrupt handler has enough
overhead to harm latency for low queue depth workloads. Complete one cycle
through the completion queue in the primary handler to ensure threaded
interrupts have no disadvantage compared to not using threaded interrupts. Wake
the thread only if more completions remain after processing the queue
once since that indicates a higher queue depth workload that may trigger
frequent interrupts which would be better completed in the handler thread
with device interrupts disabled.

Completing requests from two different contexts is safe since nvme driver
disables entry to the primary handler when it returns IRQ_WAKE_THREAD.

Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/nvme/host/pci.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index a0138e3ca0b9..e415fadf7331 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -1055,6 +1055,10 @@ static irqreturn_t nvme_irq_check(int irq, void *data)
 	if (!nvme_cqe_pending(nvmeq))
 		return IRQ_NONE;
 
+	nvme_irq(irq, data);
+	if (!nvme_cqe_pending(nvmeq))
+		return IRQ_HANDLED;
+
 	if (!to_pci_dev(nvmeq->dev->dev)->msix_enabled)
 		writel(1 << nvmeq->cq_vector, nvmeq->dev->bar + NVME_REG_INTMS);
 
-- 
2.21.0


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