[SCSI] vmw_pvscsi: Add support for I/O requests coalescing.

This change allows pvscsi driver to coalesce I/O requests
before issuing them. The number of I/O's coalesced can be
dynamically configured based on the workload.

Signed-off-by: Rishi Mehta <[e-mail]>
Signed-off-by: Arvind Kumar <[e-mail]>
Signed-off-by: James Bottomley <[e-mail]>

drivers/scsi/vmw_pvscsi.c

···
 	bool				use_msi;
 	bool				use_msix;
 	bool				use_msg;
+	bool				use_req_threshold;
 
 	spinlock_t			hw_lock;
 
···
 static bool pvscsi_disable_msi;
 static bool pvscsi_disable_msix;
 static bool pvscsi_use_msg       = true;
+static bool pvscsi_use_req_threshold = true;
 
 #define PVSCSI_RW (S_IRUSR | S_IWUSR)
 
···
 
 module_param_named(use_msg, pvscsi_use_msg, bool, PVSCSI_RW);
 MODULE_PARM_DESC(use_msg, "Use msg ring when available - (default=1)");
+
+module_param_named(use_req_threshold, pvscsi_use_req_threshold,
+		   bool, PVSCSI_RW);
+MODULE_PARM_DESC(use_req_threshold, "Use driver-based request coalescing if configured - (default=1)");
 
 static const struct pci_device_id pvscsi_pci_tbl[] = {
 	{ PCI_VDEVICE(VMWARE, PCI_DEVICE_ID_VMWARE_PVSCSI) },
···
 static void pvscsi_kick_io(const struct pvscsi_adapter *adapter,
 			   unsigned char op)
 {
-	if (scsi_is_rw(op))
-		pvscsi_kick_rw_io(adapter);
-	else
+	if (scsi_is_rw(op)) {
+		struct PVSCSIRingsState *s = adapter->rings_state;
+
+		if (!adapter->use_req_threshold ||
+		    s->reqProdIdx - s->reqConsIdx >= s->reqCallThreshold)
+			pvscsi_kick_rw_io(adapter);
+	} else {
 		pvscsi_process_request_ring(adapter);
+	}
 }
 
 static void ll_adapter_reset(const struct pvscsi_adapter *adapter)
···
 	return 1;
 }
 
+static bool pvscsi_setup_req_threshold(struct pvscsi_adapter *adapter,
+				      bool enable)
+{
+	u32 val;
+
+	if (!pvscsi_use_req_threshold)
+		return false;
+
+	pvscsi_reg_write(adapter, PVSCSI_REG_OFFSET_COMMAND,
+			 PVSCSI_CMD_SETUP_REQCALLTHRESHOLD);
+	val = pvscsi_reg_read(adapter, PVSCSI_REG_OFFSET_COMMAND_STATUS);
+	if (val == -1) {
+		printk(KERN_INFO "vmw_pvscsi: device does not support req_threshold\n");
+		return false;
+	} else {
+		struct PVSCSICmdDescSetupReqCall cmd_msg = { 0 };
+		cmd_msg.enable = enable;
+		printk(KERN_INFO
+		       "vmw_pvscsi: %sabling reqCallThreshold\n",
+			enable ? "en" : "dis");
+		pvscsi_write_cmd_desc(adapter,
+				      PVSCSI_CMD_SETUP_REQCALLTHRESHOLD,
+				      &cmd_msg, sizeof(cmd_msg));
+		return pvscsi_reg_read(adapter,
+				       PVSCSI_REG_OFFSET_COMMAND_STATUS) != 0;
+	}
+}
+
 static irqreturn_t pvscsi_isr(int irq, void *devp)
 {
 	struct pvscsi_adapter *adapter = devp;
···
 		adapter->irq = pdev->irq;
 		flags = IRQF_SHARED;
 	}
+
+	adapter->use_req_threshold = pvscsi_setup_req_threshold(adapter, true);
+	printk(KERN_DEBUG "vmw_pvscsi: driver-based request coalescing %sabled\n",
+	       adapter->use_req_threshold ? "en" : "dis");
 
 	error = request_irq(adapter->irq, pvscsi_isr, flags,
 			    "vmw_pvscsi", adapter);

drivers/scsi/vmw_pvscsi.h

···
 
 #include <linux/types.h>
 
-#define PVSCSI_DRIVER_VERSION_STRING   "1.0.3.0-k"
+#define PVSCSI_DRIVER_VERSION_STRING   "1.0.4.0-k"
 
 #define PVSCSI_MAX_NUM_SG_ENTRIES_PER_SEGMENT 128
 
···
 	PVSCSI_CMD_CONFIG            = 7,
 	PVSCSI_CMD_SETUP_MSG_RING    = 8,
 	PVSCSI_CMD_DEVICE_UNPLUG     = 9,
+	PVSCSI_CMD_SETUP_REQCALLTHRESHOLD     = 10,
 
-	PVSCSI_CMD_LAST              = 10  /* has to be last */
+	PVSCSI_CMD_LAST              = 11  /* has to be last */
 };
 
 /*
···
 	u64 configPageAddress;
 	u32 configPageNum;
 	u32 _pad;
+} __packed;
+
+/*
+ * Command descriptor for PVSCSI_CMD_SETUP_REQCALLTHRESHOLD --
+ */
+
+struct PVSCSICmdDescSetupReqCall {
+	u32 enable;
 } __packed;
 
 enum PVSCSIConfigPageType {
···
 	u32	cmpConsIdx;
 	u32	cmpNumEntriesLog2;
 
-	u8	_pad[104];
+	u32	reqCallThreshold;
+
+	u8	_pad[100];
 
 	u32	msgProdIdx;
 	u32	msgConsIdx;