scsi: storvsc: Size the queue depth based on the ringbuffer size

Size the queue depth based on the ringbuffer size. Also accommodate for the
fact that we could have multiple channels (ringbuffers) per adaptor.
Signed-off-by: NK. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: NLong Li <longli@microsoft.com>
Signed-off-by: NJames Bottomley <JBottomley@Odin.com>

drivers/scsi/storvsc_drv.c

@@ -309,10 +309,15 @@ enum storvsc_request_type {
  */
 
 static int storvsc_ringbuffer_size = (256 * PAGE_SIZE);
+static u32 max_outstanding_req_per_channel;
+
+static int storvsc_vcpus_per_sub_channel = 4;
 
 module_param(storvsc_ringbuffer_size, int, S_IRUGO);
 MODULE_PARM_DESC(storvsc_ringbuffer_size, "Ring buffer size (bytes)");
 
+module_param(storvsc_vcpus_per_sub_channel, int, S_IRUGO);
+MODULE_PARM_DESC(vcpus_per_sub_channel, "Ratio of VCPUs to subchannels");
 /*
  * Timeout in seconds for all devices managed by this driver.
  */
@@ -320,7 +325,6 @@ static int storvsc_timeout = 180;
 
 static int msft_blist_flags = BLIST_TRY_VPD_PAGES;
 
-#define STORVSC_MAX_IO_REQUESTS				200
 
 static void storvsc_on_channel_callback(void *context);
 
@@ -1376,7 +1380,6 @@ static int storvsc_do_io(struct hv_device *device,
 
 static int storvsc_device_configure(struct scsi_device *sdevice)
 {
-	scsi_change_queue_depth(sdevice, STORVSC_MAX_IO_REQUESTS);
 
 	blk_queue_max_segment_size(sdevice->request_queue, PAGE_SIZE);
 
@@ -1646,7 +1649,6 @@ static struct scsi_host_template scsi_driver = {
 	.eh_timed_out =		storvsc_eh_timed_out,
 	.slave_configure =	storvsc_device_configure,
 	.cmd_per_lun =		255,
-	.can_queue =		STORVSC_MAX_IO_REQUESTS*STORVSC_MAX_TARGETS,
 	.this_id =		-1,
 	/* no use setting to 0 since ll_blk_rw reset it to 1 */
 	/* currently 32 */
@@ -1686,6 +1688,7 @@ static int storvsc_probe(struct hv_device *device,
 			const struct hv_vmbus_device_id *dev_id)
 {
 	int ret;
+	int num_cpus = num_online_cpus();
 	struct Scsi_Host *host;
 	struct hv_host_device *host_dev;
 	bool dev_is_ide = ((dev_id->driver_data == IDE_GUID) ? true : false);
@@ -1694,6 +1697,7 @@ static int storvsc_probe(struct hv_device *device,
 	int max_luns_per_target;
 	int max_targets;
 	int max_channels;
+	int max_sub_channels = 0;
 
 	/*
 	 * Based on the windows host we are running on,
@@ -1719,12 +1723,18 @@ static int storvsc_probe(struct hv_device *device,
 		max_luns_per_target = STORVSC_MAX_LUNS_PER_TARGET;
 		max_targets = STORVSC_MAX_TARGETS;
 		max_channels = STORVSC_MAX_CHANNELS;
+		/*
+		 * On Windows8 and above, we support sub-channels for storage.
+		 * The number of sub-channels offerred is based on the number of
+		 * VCPUs in the guest.
+		 */
+		max_sub_channels = (num_cpus / storvsc_vcpus_per_sub_channel);
 		break;
 	}
 
-	if (dev_id->driver_data == SFC_GUID)
-		scsi_driver.can_queue = (STORVSC_MAX_IO_REQUESTS *
-					 STORVSC_FC_MAX_TARGETS);
+	scsi_driver.can_queue = (max_outstanding_req_per_channel *
+				 (max_sub_channels + 1));
+
 	host = scsi_host_alloc(&scsi_driver,
 			       sizeof(struct hv_host_device));
 	if (!host)
@@ -1837,7 +1847,6 @@ static struct hv_driver storvsc_drv = {
 
 static int __init storvsc_drv_init(void)
 {
-	u32 max_outstanding_req_per_channel;
 
 	/*
 	 * Divide the ring buffer data size (which is 1 page less
@@ -1852,10 +1861,6 @@ static int __init storvsc_drv_init(void)
 		vmscsi_size_delta,
 		sizeof(u64)));
 
-	if (max_outstanding_req_per_channel <
-	    STORVSC_MAX_IO_REQUESTS)
-		return -EINVAL;
-
 	return vmbus_driver_register(&storvsc_drv);
 }