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Commit 3eba9a77 authored by K. Y. Srinivasan's avatar K. Y. Srinivasan Committed by Greg Kroah-Hartman
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Drivers: hv: vmbus: Eliminate the spin lock on the read path 



The function hv_ringbuffer_read() is called always on a pre-assigned
CPU. Each chnnel is bound to a specific CPU and this function is
always called on the CPU the channel is bound. There is no need to
acquire the spin lock; get rid of this overhead.

Signed-off-by: default avatarK. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 85d9aa70

drivers/hv/ring_buffer.c

+5 −13
Original line number Diff line number Diff line
@@ -388,7 +388,6 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, 
	u32 bytes_avail_toread;

	u32 next_read_location = 0;

	u64 prev_indices = 0;

	unsigned long flags;

	struct vmpacket_descriptor desc;

	u32 offset;

	u32 packetlen;
@@ -397,7 +396,6 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, 
	if (buflen <= 0)

		return -EINVAL;



	spin_lock_irqsave(&inring_info->ring_lock, flags);



	*buffer_actual_len = 0;

	*requestid = 0;
@@ -412,7 +410,7 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, 
		 * No error is set when there is even no header, drivers are

		 * supposed to analyze buffer_actual_len.

		 */

		goto out_unlock;

		return ret;

	}



	next_read_location = hv_get_next_read_location(inring_info);
@@ -425,15 +423,11 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, 
	*buffer_actual_len = packetlen;

	*requestid = desc.trans_id;



	if (bytes_avail_toread < packetlen + offset) {

		ret = -EAGAIN;

		goto out_unlock;

	}

	if (bytes_avail_toread < packetlen + offset)

		return -EAGAIN;



	if (packetlen > buflen) {

		ret = -ENOBUFS;

		goto out_unlock;

	}

	if (packetlen > buflen)

		return -ENOBUFS;



	next_read_location =

		hv_get_next_readlocation_withoffset(inring_info, offset);
@@ -460,7 +454,5 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, 


	*signal = hv_need_to_signal_on_read(bytes_avail_towrite, inring_info);



out_unlock:

	spin_unlock_irqrestore(&inring_info->ring_lock, flags);

	return ret;

}