[PATCH V2 12/13] Drivers: hv: vmbus: Eliminate the spin lock on the read path

K. Y. Srinivasan
2016-01-28T04:56:30Z

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: K. Y. Srinivasan <kys@microsoft.com>
---
drivers/hv/ring_buffer.c | 18 +++++-------------
1 files changed, 5 insertions(+), 13 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index b53702c..1145f3b 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -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;
}
--
1.7.4.1