Re: [PATCH 1/6] nvme: don't disable local ints for polled queue

[Max Gurtovoy]

On 11/10/2018 5:13 PM, Jens Axboe wrote:

A polled queued doesn't trigger interrupts, so it's always safe
to grab the queue lock without disabling interrupts.

Jens,

can you share the added value in performance for this change ?

Cc: Keith Busch <keith.bu...@intel.com>
Cc: linux-n...@lists.infradead.org
Signed-off-by: Jens Axboe <ax...@kernel.dk>
---
  drivers/nvme/host/pci.c | 17 ++++++++++++++---
  1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 6aa86dfcb32c..a6e3fbddfadf 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -1061,15 +1061,26 @@ static irqreturn_t nvme_irq_check(int irq, void *data)

static int __nvme_poll(struct nvme_queue *nvmeq, unsigned int tag)

  {
+       unsigned long flags = 0; /* gcc 7.x fail */
        u16 start, end;
-       bool found;
+       bool found, has_irq;

if (!nvme_cqe_pending(nvmeq))

                return 0;

- spin_lock_irq(&nvmeq->cq_lock);

+       /*
+        * Polled queue doesn't have an IRQ, no need to disable ints
+        */
+       has_irq = !nvmeq->polled;
+       if (has_irq)
+               local_irq_save(flags);
+
+       spin_lock(&nvmeq->cq_lock);
        found = nvme_process_cq(nvmeq, &start, &end, tag);
-       spin_unlock_irq(&nvmeq->cq_lock);
+       spin_unlock(&nvmeq->cq_lock);
+
+       if (has_irq)
+               local_irq_restore(flags);

nvme_complete_cqes(nvmeq, start, end);

        return found;