Implement APIs for in-place consumption of vmbus packets. Currently, each
packet is copied and processed one at a time and as part of processing
each packet we potentially may signal the host (if it is waiting for
room to produce a packet).
These APIs help batched in-place processing of vmbus packets.
We also optimize host signaling by having a separate API to signal
the end of in-place consumption. With netvsc using these APIs,
on an iperf run on average I see about 20X reduction in checks to
signal the host.
Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
---
drivers/hv/ring_buffer.c | 1 +
include/linux/hyperv.h | 86 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 87 insertions(+), 0 deletions(-)
diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index dd255c9..fe586bf 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -132,6 +132,7 @@ hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
u32 next_read_location)
{
ring_info->ring_buffer->read_index = next_read_location;
+ ring_info->priv_read_index = next_read_location;
}
/* Get the size of the ring buffer. */
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 6797a30..b10954a 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -126,6 +126,8 @@ struct hv_ring_buffer_info {
u32 ring_datasize; /* < ring_size */
u32 ring_data_startoffset;
+ u32 priv_write_index;
+ u32 priv_read_index;
};
/*
@@ -1420,4 +1422,88 @@ static inline bool hv_need_to_signal_on_read(struct hv_ring_buffer_info *rbi)
return false;
}
+/*
+ * An API to support in-place processing of incoming VMBUS packets.
+ */
+#define VMBUS_PKT_TRAILER 8
+
+static inline struct vmpacket_descriptor *
+get_next_pkt_raw(struct vmbus_channel *channel)
+{
+ struct hv_ring_buffer_info *ring_info = &channel->inbound;
+ u32 read_loc = ring_info->priv_read_index;
+ void *ring_buffer = hv_get_ring_buffer(ring_info);
+ struct vmpacket_descriptor *cur_desc;
+ u32 packetlen;
+ u32 dsize = ring_info->ring_datasize;
+ u32 delta = read_loc - ring_info->ring_buffer->read_index;
+ u32 bytes_avail_toread = (hv_get_bytes_to_read(ring_info) - delta);
+
+ if (bytes_avail_toread < sizeof(struct vmpacket_descriptor))
+ return NULL;
+
+ if ((read_loc + sizeof(*cur_desc)) > dsize)
+ return NULL;
+
+ cur_desc = ring_buffer + read_loc;
+ packetlen = cur_desc->len8 << 3;
+
+ /*
+ * If the packet under consideration is wrapping around,
+ * return failure.
+ */
+ if ((read_loc + packetlen + VMBUS_PKT_TRAILER) > (dsize - 1))
+ return NULL;
+
+ return cur_desc;
+}
+
+/*
+ * A helper function to step through packets "in-place"
+ * This API is to be called after each successful call
+ * get_next_pkt_raw().
+ */
+static inline void put_pkt_raw(struct vmbus_channel *channel,
+ struct vmpacket_descriptor *desc)
+{
+ struct hv_ring_buffer_info *ring_info = &channel->inbound;
+ u32 read_loc = ring_info->priv_read_index;
+ u32 packetlen = desc->len8 << 3;
+ u32 dsize = ring_info->ring_datasize;
+
+ if ((read_loc + packetlen + VMBUS_PKT_TRAILER) > dsize)
+ BUG();
+ /*
+ * Include the packet trailer.
+ */
+ ring_info->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
+}
+
+/*
+ * This call commits the read index and potentially signals the host.
+ * Here is the pattern for using the "in-place" consumption APIs:
+ *
+ * while (get_next_pkt_raw() {
+ * process the packet "in-place";
+ * put_pkt_raw();
+ * }
+ * if (packets processed in place)
+ * commit_rd_index();
+ */
+static inline void commit_rd_index(struct vmbus_channel *channel)
+{
+ struct hv_ring_buffer_info *ring_info = &channel->inbound;
+ /*
+ * Make sure all reads are done before we update the read index since
+ * the writer may start writing to the read area once the read index
+ * is updated.
+ */
+ 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);
+}
+
+
#endif /* _HYPERV_H */
--
1.7.4.1
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