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: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index b53702ce692f35652c8efcb987cc0d79aa1b6fc0..1145f3b8e4e081410429b263f0abe71cac742587 100644 (file)
--- 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;
 }