From 555ce5fc0fff8fc1f40f6af1e2f251b1b4181f15 Mon Sep 17 00:00:00 2001
From: Dexuan Cui <decui@microsoft.com>
Date: Wed, 27 Jan 2016 22:29:39 -0800
Subject: [PATCH 28/44] Drivers: hv: vmbus: vmbus_sendpacket_ctl: hvsock: avoid
 unnecessary signaling

When the hvsock channel's outbound ringbuffer is full (i.e.,
hv_ringbuffer_write() returns -EAGAIN), we should avoid the unnecessary
signaling the host.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 5f363bc38f810d238d1e8b19998625ddec3b8138)
---
 drivers/hv/channel.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index def21d34f3ea..a42104ed0b59 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -661,6 +661,9 @@ int vmbus_sendpacket_ctl(struct vmbus_channel *channel, void *buffer,
 	 * If we cannot write to the ring-buffer; signal the host
 	 * even if we may not have written anything. This is a rare
 	 * enough condition that it should not matter.
+	 * NOTE: in this case, the hvsock channel is an exception, because
+	 * it looks the host side's hvsock implementation has a throttling
+	 * mechanism which can hurt the performance otherwise.
 	 */
 
 	if (channel->signal_policy)
@@ -668,7 +671,8 @@ int vmbus_sendpacket_ctl(struct vmbus_channel *channel, void *buffer,
 	else
 		kick_q = true;
 
-	if (((ret == 0) && kick_q && signal) || (ret))
+	if (((ret == 0) && kick_q && signal) ||
+	    (ret && !is_hvsock_channel(channel)))
 		vmbus_setevent(channel);
 
 	return ret;
-- 
2.13.0

