linux-kernel - [PATCH 3/6] vmbus: refactor hv_signal_on

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Message-Id: <1498419029-4127-3-git-send-email-kys@exchange.microsoft.com>
Date:   Sun, 25 Jun 2017 12:30:26 -0700
From:   kys@...hange.microsoft.com
To:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        vkuznets@...hat.com, jasowang@...hat.com,
        leann.ogasawara@...onical.com, marcelo.cerri@...onical.com,
        sthemmin@...rosoft.com
Cc:     Stephen Hemminger <stephen@...workplumber.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>
Subject: [PATCH 3/6] vmbus: refactor hv_signal_on_read

From: Stephen Hemminger <stephen@...workplumber.org>

The function hv_signal_on_read was defined in hyperv.h and
only used in one place in ring_buffer code. Clearer to just
move it inline there.

Signed-off-by: Stephen Hemminger <sthemmin@...rosoft.com>
Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
---
 drivers/hv/ring_buffer.c |   32 ++++++++++++++++++++++++++++-
 include/linux/hyperv.h   |   49 ----------------------------------------------
 2 files changed, 30 insertions(+), 51 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index f299817..a9021f1 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -29,6 +29,7 @@
 #include <linux/uio.h>
 #include <linux/vmalloc.h>
 #include <linux/slab.h>
+#include <linux/prefetch.h>
 
 #include "hyperv_vmbus.h"
 
@@ -357,7 +358,7 @@ struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
 {
 	struct hv_ring_buffer_info *rbi = &channel->inbound;
 
-	/* set state for later hv_signal_on_read() */
+	/* set state for later hv_pkt_iter_close */
 	rbi->cached_read_index = rbi->ring_buffer->read_index;
 
 	if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
@@ -400,6 +401,8 @@ struct vmpacket_descriptor *
 void hv_pkt_iter_close(struct vmbus_channel *channel)
 {
 	struct hv_ring_buffer_info *rbi = &channel->inbound;
+	u32 cur_write_sz, cached_write_sz;
+	u32 pending_sz;
 
 	/*
 	 * Make sure all reads are done before we update the read index since
@@ -409,6 +412,31 @@ void hv_pkt_iter_close(struct vmbus_channel *channel)
 	virt_rmb();
 	rbi->ring_buffer->read_index = rbi->priv_read_index;
 
-	hv_signal_on_read(channel);
+	/*
+	 * Issue a full memory barrier before making the signaling decision.
+	 * Here is the reason for having this barrier:
+	 * If the reading of the pend_sz (in this function)
+	 * were to be reordered and read before we commit the new read
+	 * index (in the calling function)  we could
+	 * have a problem. If the host were to set the pending_sz after we
+	 * have sampled pending_sz and go to sleep before we commit the
+	 * read index, we could miss sending the interrupt. Issue a full
+	 * memory barrier to address this.
+	 */
+	virt_mb();
+
+	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;
+
+	cur_write_sz = hv_get_bytes_to_write(rbi);
+
+	if (cur_write_sz < pending_sz)
+		return;
+
+	cached_write_sz = hv_get_cached_bytes_to_write(rbi);
+	if (cached_write_sz < pending_sz)
+		vmbus_setevent(channel);
 }
 EXPORT_SYMBOL_GPL(hv_pkt_iter_close);
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index b1549c9..0262267 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1458,55 +1458,6 @@ int vmbus_send_tl_connect_request(const uuid_le *shv_guest_servie_id,
 }
 
 /*
- * To optimize the flow management on the send-side,
- * when the sender is blocked because of lack of
- * sufficient space in the ring buffer, potential the
- * consumer of the ring buffer can signal the producer.
- * This is controlled by the following parameters:
- *
- * 1. pending_send_sz: This is the size in bytes that the
- *    producer is trying to send.
- * 2. The feature bit feat_pending_send_sz set to indicate if
- *    the consumer of the ring will signal when the ring
- *    state transitions from being full to a state where
- *    there is room for the producer to send the pending packet.
- */
-
-static inline  void hv_signal_on_read(struct vmbus_channel *channel)
-{
-	u32 cur_write_sz, cached_write_sz;
-	u32 pending_sz;
-	struct hv_ring_buffer_info *rbi = &channel->inbound;
-
-	/*
-	 * Issue a full memory barrier before making the signaling decision.
-	 * Here is the reason for having this barrier:
-	 * If the reading of the pend_sz (in this function)
-	 * were to be reordered and read before we commit the new read
-	 * index (in the calling function)  we could
-	 * have a problem. If the host were to set the pending_sz after we
-	 * have sampled pending_sz and go to sleep before we commit the
-	 * read index, we could miss sending the interrupt. Issue a full
-	 * memory barrier to address this.
-	 */
-	virt_mb();
-
-	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;
-
-	cur_write_sz = hv_get_bytes_to_write(rbi);
-
-	if (cur_write_sz < pending_sz)
-		return;
-
-	cached_write_sz = hv_get_cached_bytes_to_write(rbi);
-	if (cached_write_sz < pending_sz)
-		vmbus_setevent(channel);
-}
-
-/*
  * Mask off host interrupt callback notifications
  */
 static inline void hv_begin_read(struct hv_ring_buffer_info *rbi)
-- 
1.7.1