Re: [PATCH 1/1] net/hyperv: Add flow control based on hi/low watermark

In the existing code, we only stop queue when the ringbuffer is full,
so the current packet has to be dropped or retried from upper layer.

This patch stops the tx queue when available ringbuffer is below
the low watermark. So the ringbuffer still has small amount of space
available for the current packet. This will reduce the overhead of
retries on sending.

Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: K. Y. Srinivasan <kys@microsoft.com>
---
 drivers/hv/ring_buffer.c        |   15 +++++++++++++++
 drivers/net/hyperv/hyperv_net.h |    3 +++
 drivers/net/hyperv/netvsc.c     |   23 +++++++++++++++++++----
 drivers/net/hyperv/netvsc_drv.c |   16 +++++++++++++++-
 include/linux/hyperv.h          |    3 +++
 5 files changed, 55 insertions(+), 5 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 8af25a0..8cc3f63 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c

@@ -23,6 +23,7 @@
  */
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
 #include <linux/hyperv.h>

@@ -160,6 +161,20 @@ hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
 }
 
 /*
+ * Get the percentage of available bytes to write in the ring.
+ * The return value is in range from 0 to 100.
+ */
+u32 hv_ringbuf_avail_percent(struct hv_ring_buffer_info *ring_info)
+{
+	u32 avail_read, avail_write;
+
+	hv_get_ringbuffer_availbytes(ring_info, &avail_read, &avail_write);
+
+	return avail_write * 100 / hv_get_ring_buffersize(ring_info);
+}
+EXPORT_SYMBOL(hv_ringbuf_avail_percent);

--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c

@@ -51,6 +51,16 @@ static int ring_size = 128;
 module_param(ring_size, int, S_IRUGO);
 MODULE_PARM_DESC(ring_size, "Ring buffer size (# of pages)");
 
+uint ring_avail_percent_hiwater = 20;
+module_param(ring_avail_percent_hiwater, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(ring_avail_percent_hiwater,
+	"Ring buffer available percentiles to wake up xmit queue");
+
+uint ring_avail_percent_lowater = 10;
+module_param(ring_avail_percent_lowater, uint, S_IRUGO | S_IWUSR);
+MODULE_PARM_DESC(ring_avail_percent_lowater,
+	"Ring buffer available percentiles to stop xmit queue");