[PATCH v4] net: netvsc: Update default VMBus channels

[Erni Sri Satya Vennela <ernis@linux.microsoft.com>]

Change VMBus channels macro (VRSS_CHANNEL_DEFAULT) in
Linux netvsc from 8 to 16 to align with Azure Windows VM
and improve networking throughput.

For VMs having less than 16 vCPUS, the channels depend
on number of vCPUs. For greater than 16 vCPUs,
set the channels to maximum of VRSS_CHANNEL_DEFAULT and
number of physical cores / 2 which is returned by
netif_get_num_default_rss_queues() as a way to optimize CPU
resource utilization and scale for high-end processors with
many cores.
Maximum number of channels are by default set to 64.

Based on this change the channel creation would change as follows:

-----------------------------------------------------------------
| No. of vCPU |  dev_info->num_chn |    channels created        |
-----------------------------------------------------------------
|    1-16     |        16	   |          vCPU              |
|    >16      |  max(16,#cores/2)  | min(64 , max(16,#cores/2)) |
-----------------------------------------------------------------

Performance tests showed significant improvement in throughput:
- 0.54% for 16 vCPUs
- 0.83% for 32 vCPUs
- 0.86% for 48 vCPUs
- 9.72% for 64 vCPUs
- 13.57% for 96 vCPUs

Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
---
Changes in v4:
* Update commit message for channels created
---
Changes in v3:
* Use netif_get_num_default_rss_queues() to set channels
* Change terminology for channels in commit message
---
Changes in v2:
* Set dev_info->num_chn based on vCPU count.
---
 drivers/net/hyperv/hyperv_net.h | 2 +-
 drivers/net/hyperv/netvsc_drv.c | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hyperv/hyperv_net.h b/drivers/net/hyperv/hyperv_net.h
index 810977952f95..e690b95b1bbb 100644
--- a/drivers/net/hyperv/hyperv_net.h
+++ b/drivers/net/hyperv/hyperv_net.h
@@ -882,7 +882,7 @@ struct nvsp_message {
 
 #define VRSS_SEND_TAB_SIZE 16  /* must be power of 2 */
 #define VRSS_CHANNEL_MAX 64
-#define VRSS_CHANNEL_DEFAULT 8
+#define VRSS_CHANNEL_DEFAULT 16
 
 #define RNDIS_MAX_PKT_DEFAULT 8
 #define RNDIS_PKT_ALIGN_DEFAULT 8
diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 44142245343d..a6482afe4217 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -987,7 +987,8 @@ struct netvsc_device_info *netvsc_devinfo_get(struct netvsc_device *nvdev)
 			dev_info->bprog = prog;
 		}
 	} else {
-		dev_info->num_chn = VRSS_CHANNEL_DEFAULT;
+		dev_info->num_chn = max(VRSS_CHANNEL_DEFAULT,
+					netif_get_num_default_rss_queues());
 		dev_info->send_sections = NETVSC_DEFAULT_TX;
 		dev_info->send_section_size = NETVSC_SEND_SECTION_SIZE;
 		dev_info->recv_sections = NETVSC_DEFAULT_RX;
-- 
2.34.1