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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: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
K. Y. Srinivasan 2016-01-27 22:29:44 -08:00 committed by Greg Kroah-Hartman
parent 85d9aa7051
commit 3eba9a77d5
1 changed files with 5 additions and 13 deletions
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18
drivers/hv/ring_buffer.c
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@ -388,7 +388,6 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
u32 bytes_avail_toread; u32 bytes_avail_toread;
u32 next_read_location = 0; u32 next_read_location = 0;
u64 prev_indices = 0; u64 prev_indices = 0;
unsigned long flags;
struct vmpacket_descriptor desc; struct vmpacket_descriptor desc;
u32 offset; u32 offset;
u32 packetlen; u32 packetlen;
@ -397,7 +396,6 @@ int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info,
if (buflen <= 0) if (buflen <= 0)
return -EINVAL; return -EINVAL;
spin_lock_irqsave(&inring_info->ring_lock, flags);
*buffer_actual_len = 0; *buffer_actual_len = 0;
*requestid = 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 * No error is set when there is even no header, drivers are
* supposed to analyze buffer_actual_len. * supposed to analyze buffer_actual_len.
*/ */
goto out_unlock; return ret;
} }
next_read_location = hv_get_next_read_location(inring_info); 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; *buffer_actual_len = packetlen;
*requestid = desc.trans_id; *requestid = desc.trans_id;
if (bytes_avail_toread < packetlen + offset) { if (bytes_avail_toread < packetlen + offset)
ret = -EAGAIN; return -EAGAIN;
goto out_unlock;
}
if (packetlen > buflen) { if (packetlen > buflen)
ret = -ENOBUFS; return -ENOBUFS;
goto out_unlock;
}
next_read_location = next_read_location =
hv_get_next_readlocation_withoffset(inring_info, offset); 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); *signal = hv_need_to_signal_on_read(bytes_avail_towrite, inring_info);
out_unlock:
spin_unlock_irqrestore(&inring_info->ring_lock, flags);
return ret; return ret;
} }