[PATCH 26/28] Drivers: hv: Implement flow management on the send side

K. Y. Srinivasan
2012-12-01T14:24:15Z

Implement flow management on the send side. When the sender is blocked, the reader
can potentially signal the sender to indicate there is now room to send.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
---
drivers/hv/channel.c | 12 ++++++++-
drivers/hv/hyperv_vmbus.h | 2 +-
drivers/hv/ring_buffer.c | 51 ++++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 61 insertions(+), 4 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 9303252..064257e 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -735,6 +735,7 @@ int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,
u32 packetlen;
u32 userlen;
int ret;
+ bool signal = false;

*buffer_actual_len = 0;
*requestid = 0;
@@ -761,8 +762,10 @@ int vmbus_recvpacket(struct vmbus_channel *channel, void *buffer,

/* Copy over the packet to the user buffer */
ret = hv_ringbuffer_read(&channel->inbound, buffer, userlen,
- (desc.offset8 << 3));
+ (desc.offset8 << 3), &signal);

+ if (signal)
+ vmbus_setevent(channel);

return 0;
}
@@ -779,6 +782,7 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
u32 packetlen;
u32 userlen;
int ret;
+ bool signal = false;

*buffer_actual_len = 0;
*requestid = 0;
@@ -805,7 +809,11 @@ int vmbus_recvpacket_raw(struct vmbus_channel *channel, void *buffer,
*requestid = desc.trans_id;

/* Copy over the entire packet to the user buffer */
- ret = hv_ringbuffer_read(&channel->inbound, buffer, packetlen, 0);
+ ret = hv_ringbuffer_read(&channel->inbound, buffer, packetlen, 0,
+ &signal);
+
+ if (signal)
+ vmbus_setevent(channel);

return 0;
}
diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index becb106..ac111f2 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -550,7 +550,7 @@ int hv_ringbuffer_peek(struct hv_ring_buffer_info *ring_info, void *buffer,
int hv_ringbuffer_read(struct hv_ring_buffer_info *ring_info,
void *buffer,
u32 buflen,
- u32 offset);
+ u32 offset, bool *signal);

void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 2a0babc..cafa72f 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -84,6 +84,50 @@ static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
return false;
}

+/*
+ * 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 bool hv_need_to_signal_on_read(u32 old_rd,
+ struct hv_ring_buffer_info *rbi)
+{
+ u32 prev_write_sz;
+ u32 cur_write_sz;
+ u32 r_size;
+ u32 write_loc = rbi->ring_buffer->write_index;
+ u32 read_loc = rbi->ring_buffer->read_index;
+ u32 pending_sz = rbi->ring_buffer->pending_send_sz;
+
+ /*
+ * If the other end is not blocked on write don't bother.
+ */
+ if (pending_sz == 0)
+ return false;
+
+ r_size = rbi->ring_datasize;
+ cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
+ read_loc - write_loc;
+
+ prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
+ old_rd - write_loc;
+
+
+ if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
+ return true;
+
+ return false;
+}

/*
* hv_get_next_write_location()
@@ -461,13 +505,14 @@ int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
*
*/
int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
- u32 buflen, u32 offset)
+ u32 buflen, u32 offset, bool *signal)
{
u32 bytes_avail_towrite;
u32 bytes_avail_toread;
u32 next_read_location = 0;
u64 prev_indices = 0;
unsigned long flags;
+ u32 old_read;

if (buflen <= 0)
return -EINVAL;
@@ -478,6 +523,8 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
&bytes_avail_toread,
&bytes_avail_towrite);

+ old_read = bytes_avail_toread;
+
/* Make sure there is something to read */
if (bytes_avail_toread < buflen) {
spin_unlock_irqrestore(&inring_info->ring_lock, flags);
@@ -508,5 +555,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,

spin_unlock_irqrestore(&inring_info->ring_lock, flags);

+ *signal = hv_need_to_signal_on_read(old_read, inring_info);
+
return 0;
}
--
1.7.4.1