NVMe: Restructure MSI / MSI-X setup

The current code copies 'nr_io_queues' into 'q_count', modifies
'nr_io_queues' during MSI-X setup, then resets 'nr_io_queues' for
MSI setup.  Instead, copy 'nr_io_queues' into 'vecs' and modify 'vecs'
during both MSI-X and MSI setup.

This lets us simplify the for-loops that set up MSI-X and MSI, and opens
the possibility of using more I/O queues than we have interrupt vectors,
should future benchmarking prove that to be a useful feature.

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>

diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
index ce79a59..de3a759 100644 (file)
--- a/drivers/block/nvme-core.c
+++ b/drivers/block/nvme-core.c
@@ -1638,7 +1638,7 @@ static int set_queue_count(struct nvme_dev *dev, int count)
 static int nvme_setup_io_queues(struct nvme_dev *dev)
 {
        struct pci_dev *pdev = dev->pci_dev;
-       int result, cpu, i, nr_io_queues, db_bar_size, q_depth, q_count;
+       int result, cpu, i, vecs, nr_io_queues, db_bar_size, q_depth;
 
        nr_io_queues = num_online_cpus();
        result = set_queue_count(dev, nr_io_queues);
@@ -1647,7 +1647,6 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
        if (result < nr_io_queues)
                nr_io_queues = result;
 
-       q_count = nr_io_queues;
        /* Deregister the admin queue's interrupt */
        free_irq(dev->entry[0].vector, dev->queues[0]);
 
@@ -1659,39 +1658,42 @@ static int nvme_setup_io_queues(struct nvme_dev *dev)
                dev->queues[0]->q_db = dev->dbs;
        }
 
-       for (i = 0; i < nr_io_queues; i++)
+       vecs = nr_io_queues;
+       for (i = 0; i < vecs; i++)
                dev->entry[i].entry = i;
        for (;;) {
-               result = pci_enable_msix(pdev, dev->entry, nr_io_queues);
-               if (result == 0) {
+               result = pci_enable_msix(pdev, dev->entry, vecs);
+               if (result <= 0)
                        break;
-               } else if (result > 0) {
-                       nr_io_queues = result;
-                       continue;
-               } else {
-                       nr_io_queues = 0;
-                       break;
-               }
+               vecs = result;
        }
 
-       if (nr_io_queues == 0) {
-               nr_io_queues = q_count;
+       if (result < 0) {
+               vecs = nr_io_queues;
+               if (vecs > 32)
+                       vecs = 32;
                for (;;) {
-                       result = pci_enable_msi_block(pdev, nr_io_queues);
+                       result = pci_enable_msi_block(pdev, vecs);
                        if (result == 0) {
-                               for (i = 0; i < nr_io_queues; i++)
+                               for (i = 0; i < vecs; i++)
                                        dev->entry[i].vector = i + pdev->irq;
                                break;
-                       } else if (result > 0) {
-                               nr_io_queues = result;
-                               continue;
-                       } else {
-                               nr_io_queues = 1;
+                       } else if (result < 0) {
+                               vecs = 1;
                                break;
                        }
+                       vecs = result;
                }
        }
 
+       /*
+        * Should investigate if there's a performance win from allocating
+        * more queues than interrupt vectors; it might allow the submission
+        * path to scale better, even if the receive path is limited by the
+        * number of interrupts.
+        */
+       nr_io_queues = vecs;
+
        result = queue_request_irq(dev, dev->queues[0], "nvme admin");
        /* XXX: handle failure here */