NVMe: Add a module parameter to use a threaded interrupt
We're currently calling bio_endio from hard interrupt context. This is
not a good idea for preemptible kernels as it will cause longer latencies.
Using a threaded interrupt will run the entire queue processing mechanism
(including bio_endio) in a thread, which can be preempted. Unfortuantely,
it also adds about 7us of latency to the single-I/O case, so make it a
module parameter for the moment.
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
diff --git a/drivers/block/nvme.c b/drivers/block/nvme.c
index 1c3cd6c..60c3786 100644
--- a/drivers/block/nvme.c
+++ b/drivers/block/nvme.c
@@ -44,6 +44,9 @@
static int nvme_major;
module_param(nvme_major, int, 0);
+static int use_threaded_interrupts;
+module_param(use_threaded_interrupts, int, 0);
+
/*
* Represents an NVM Express device. Each nvme_dev is a PCI function.
*/
@@ -455,6 +458,25 @@
return nvme_process_cq(data);
}
+static irqreturn_t nvme_irq_thread(int irq, void *data)
+{
+ irqreturn_t result;
+ struct nvme_queue *nvmeq = data;
+ spin_lock(&nvmeq->q_lock);
+ result = nvme_process_cq(nvmeq);
+ spin_unlock(&nvmeq->q_lock);
+ return result;
+}
+
+static irqreturn_t nvme_irq_check(int irq, void *data)
+{
+ struct nvme_queue *nvmeq = data;
+ struct nvme_completion cqe = nvmeq->cqes[nvmeq->cq_head];
+ if ((le16_to_cpu(cqe.status) & 1) != nvmeq->cq_phase)
+ return IRQ_NONE;
+ return IRQ_WAKE_THREAD;
+}
+
static void nvme_abort_command(struct nvme_queue *nvmeq, int cmdid)
{
spin_lock_irq(&nvmeq->q_lock);
@@ -630,6 +652,11 @@
static int queue_request_irq(struct nvme_dev *dev, struct nvme_queue *nvmeq,
const char *name)
{
+ if (use_threaded_interrupts)
+ return request_threaded_irq(dev->entry[nvmeq->cq_vector].vector,
+ nvme_irq_check, nvme_irq_thread,
+ IRQF_DISABLED | IRQF_SHARED,
+ name, nvmeq);
return request_irq(dev->entry[nvmeq->cq_vector].vector, nvme_irq,
IRQF_DISABLED | IRQF_SHARED, name, nvmeq);
}