dmaengine: idxd: remove MSIX masking for interrupt handlers

Remove interrupt masking and just let the hard irq handler keep
firing for new events. This is less of a performance impact vs
the MMIO readback inside the pci_msi_{mask,unmas}_irq(). Especially
with a loaded system those flushes can be stuck behind large amounts
of MMIO writes to flush. When guest kernel is running on top of VFIO
mdev, mask/unmask causes a vmexit each time and is not desirable.

Suggested-by: Dan Williams <[email protected]>
Signed-off-by: Dave Jiang <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Link: https://lore.kernel.org/r/161894523436.3210025.1834640110556139277.stgit@djiang5-desk3.ch.intel.com
Signed-off-by: Vinod Koul <[email protected]>

Author: davejiang

drivers/dma/idxd/idxd.h

@@ -377,7 +377,6 @@ void idxd_wqs_quiesce(struct idxd_device *idxd);
 /* device interrupt control */
 void idxd_msix_perm_setup(struct idxd_device *idxd);
 void idxd_msix_perm_clear(struct idxd_device *idxd);
-irqreturn_t idxd_irq_handler(int vec, void *data);
 irqreturn_t idxd_misc_thread(int vec, void *data);
 irqreturn_t idxd_wq_thread(int irq, void *data);
 void idxd_mask_error_interrupts(struct idxd_device *idxd);

drivers/dma/idxd/init.c

@@ -102,7 +102,7 @@ static int idxd_setup_interrupts(struct idxd_device *idxd)
 	}
 
 	irq_entry = &idxd->irq_entries[0];
-	rc = request_threaded_irq(irq_entry->vector, idxd_irq_handler, idxd_misc_thread,
+	rc = request_threaded_irq(irq_entry->vector, NULL, idxd_misc_thread,
 				  0, "idxd-misc", irq_entry);
 	if (rc < 0) {
 		dev_err(dev, "Failed to allocate misc interrupt.\n");
@@ -119,7 +119,7 @@ static int idxd_setup_interrupts(struct idxd_device *idxd)
 
 		init_llist_head(&idxd->irq_entries[i].pending_llist);
 		INIT_LIST_HEAD(&idxd->irq_entries[i].work_list);
-		rc = request_threaded_irq(irq_entry->vector, idxd_irq_handler,
+		rc = request_threaded_irq(irq_entry->vector, NULL,
 					  idxd_wq_thread, 0, "idxd-portal", irq_entry);
 		if (rc < 0) {
 			dev_err(dev, "Failed to allocate irq %d.\n", irq_entry->vector);

drivers/dma/idxd/irq.c

@@ -102,15 +102,6 @@ static int idxd_device_schedule_fault_process(struct idxd_device *idxd,
 	return 0;
 }
 
-irqreturn_t idxd_irq_handler(int vec, void *data)
-{
-	struct idxd_irq_entry *irq_entry = data;
-	struct idxd_device *idxd = irq_entry->idxd;
-
-	idxd_mask_msix_vector(idxd, irq_entry->id);
-	return IRQ_WAKE_THREAD;
-}
-
 static int process_misc_interrupts(struct idxd_device *idxd, u32 cause)
 {
 	struct device *dev = &idxd->pdev->dev;
@@ -237,7 +228,6 @@ irqreturn_t idxd_misc_thread(int vec, void *data)
 			iowrite32(cause, idxd->reg_base + IDXD_INTCAUSE_OFFSET);
 	}
 
-	idxd_unmask_msix_vector(idxd, irq_entry->id);
 	return IRQ_HANDLED;
 }
 
@@ -394,8 +384,6 @@ irqreturn_t idxd_wq_thread(int irq, void *data)
 	int processed;
 
 	processed = idxd_desc_process(irq_entry);
-	idxd_unmask_msix_vector(irq_entry->idxd, irq_entry->id);
-
 	if (processed == 0)
 		return IRQ_NONE;