From: kys@exchange.microsoft.com
To: gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org,
        devel@linuxdriverproject.org, olaf@aepfle.de, apw@canonical.com,
        vkuznets@redhat.com, jasowang@redhat.com,
        leann.ogasawara@canonical.com, sthemmin@microsoft.com
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Subject: [PATCH V2 14/14] Drivers: hv: vmbus: On the read path cleanup the logic to interrupt the host
Date: Tue,  1 Nov 2016 13:07:34 -0700
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From: K. Y. Srinivasan <kys@microsoft.com>

Signal the host when we determine the host is to be signaled -
on th read path. The currrent code determines the need to signal in the
ringbuffer code and actually issues the signal elsewhere. This can result
in the host viewing this interrupt as spurious since the host may also
poll the channel. Make the necessary adjustments.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
 drivers/hv/channel.c      |   11 ++---------
 drivers/hv/hyperv_vmbus.h |    4 ++--
 drivers/hv/ring_buffer.c  |    7 ++++---
 include/linux/hyperv.h    |   12 ++++++------
 4 files changed, 14 insertions(+), 20 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 8a8148f..5fb4c6d 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -879,16 +879,9 @@ int vmbus_sendpacket_multipagebuffer(struct vmbus_channel *channel,
 		   u32 bufferlen, u32 *buffer_actual_len, u64 *requestid,
 		   bool raw)
 {
-	int ret;
-	bool signal = false;
-
-	ret = hv_ringbuffer_read(&channel->inbound, buffer, bufferlen,
-				 buffer_actual_len, requestid, &signal, raw);
+	return hv_ringbuffer_read(channel, buffer, bufferlen,
+				  buffer_actual_len, requestid, raw);
 
-	if (signal)
-		vmbus_setevent(channel);
-
-	return ret;
 }
 
 int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index 2d42ebe..0675b39 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -532,9 +532,9 @@ int hv_ringbuffer_write(struct vmbus_channel *channel,
 		    u32 kv_count, bool lock,
 		    bool kick_q);
 
-int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
+int hv_ringbuffer_read(struct vmbus_channel *channel,
 		       void *buffer, u32 buflen, u32 *buffer_actual_len,
-		       u64 *requestid, bool *signal, bool raw);
+		       u64 *requestid, bool raw);
 
 void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 			    struct hv_ring_buffer_debug_info *debug_info);
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 4af7130..cd49cb1 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -353,9 +353,9 @@ int hv_ringbuffer_write(struct vmbus_channel *channel,
 	return 0;
 }
 
-int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
+int hv_ringbuffer_read(struct vmbus_channel *channel,
 		       void *buffer, u32 buflen, u32 *buffer_actual_len,
-		       u64 *requestid, bool *signal, bool raw)
+		       u64 *requestid, bool raw)
 {
 	u32 bytes_avail_toread;
 	u32 next_read_location = 0;
@@ -364,6 +364,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
 	u32 offset;
 	u32 packetlen;
 	int ret = 0;
+	struct hv_ring_buffer_info *inring_info = &channel->inbound;
 
 	if (buflen <= 0)
 		return -EINVAL;
@@ -421,7 +422,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
 	/* Update the read index */
 	hv_set_next_read_location(inring_info, next_read_location);
 
-	*signal = hv_need_to_signal_on_read(inring_info);
+	hv_signal_on_read(channel);
 
 	return ret;
 }
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 8cf78ed..fdb0a87 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1487,10 +1487,11 @@ int vmbus_send_tl_connect_request(const uuid_le *shv_guest_servie_id,
  *    there is room for the producer to send the pending packet.
  */
 
-static inline  bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
+static inline  void hv_signal_on_read(struct vmbus_channel *channel)
 {
 	u32 cur_write_sz;
 	u32 pending_sz;
+	struct hv_ring_buffer_info *rbi = &channel->inbound;
 
 	/*
 	 * Issue a full memory barrier before making the signaling decision.
@@ -1508,14 +1509,14 @@ static inline  bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
 	pending_sz = READ_ONCE(rbi->ring_buffer->pending_send_sz);
 	/* If the other end is not blocked on write don't bother. */
 	if (pending_sz == 0)
-		return false;
+		return;
 
 	cur_write_sz = hv_get_bytes_to_write(rbi);
 
 	if (cur_write_sz >= pending_sz)
-		return true;
+		vmbus_setevent(channel);
 
-	return false;
+	return;
 }
 
 /*
@@ -1587,8 +1588,7 @@ static inline void commit_rd_index(struct vmbus_channel *channel)
 	virt_rmb();
 	ring_info->ring_buffer->read_index = ring_info->priv_read_index;
 
-	if (hv_need_to_signal_on_read(ring_info))
-		vmbus_set_event(channel);
+	hv_signal_on_read(channel);
 }
 
 
-- 
1.7.4.1