Commit ab028db4 authored by K. Y. Srinivasan's avatar K. Y. Srinivasan Committed by Greg Kroah-Hartman
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Drivers: hv: vmbus: Implement APIs to support "in place" consumption of vmbus packets 



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: default avatarK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 687f32e6

drivers/hv/ring_buffer.c

+1 −0
Original line number Diff line number Diff line
@@ -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. */

include/linux/hyperv.h

+86 −0
Original line number Diff line number Diff line
@@ -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 */

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