[Patch] vmbus: Simply hv_get_next_write_location() function

[Patch] vmbus: Simply hv_get_next_write_location() function

[lantianyu1986]

From: Tianyu Lan <Tianyu.Lan@microsoft.com>

The "next" variable is redundant in hv_get_next_write_location().
This patch is to remove it and return write_index directly.

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
 drivers/hv/ring_buffer.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
index 12eb8ca..71558e7 100644
--- a/drivers/hv/ring_buffer.c
+++ b/drivers/hv/ring_buffer.c
@@ -82,9 +82,7 @@ static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
 static inline u32
 hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
 {
-	u32 next = ring_info->ring_buffer->write_index;
-
-	return next;
+	return ring_info->ring_buffer->write_index;
 }
 
 /* Set the next write location for the specified ring buffer. */
-- 
2.7.4

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Re: [Patch] vmbus: Simply hv_get_next_write_location() function

[Stephen Hemminger]

On Wed, 24 Jan 2018 14:21:30 +0800
lantianyu1986@gmail.com wrote:

> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
> 
> The "next" variable is redundant in hv_get_next_write_location().
> This patch is to remove it and return write_index directly.
> 
> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
> ---
>  drivers/hv/ring_buffer.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 12eb8ca..71558e7 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -82,9 +82,7 @@ static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
>  static inline u32
>  hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
>  {
> -	u32 next = ring_info->ring_buffer->write_index;
> -
> -	return next;
> +	return ring_info->ring_buffer->write_index;
>  }
>  
>  /* Set the next write location for the specified ring buffer. */

Looks good.
But let's go farther since function is only used in one location in the file
just eliminate it completely and do simple variable references.

The get/set functions in this file are unnecessary.

Better still it is possible to replace the lock based ring structure
with a compare-exchange solution.
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Re: [Patch] vmbus: Simply hv_get_next_write_location() function

[Tianyu Lan]

On Thu, Jan 25, 2018 at 12:37 AM, Stephen Hemminger
<stephen@networkplumber.org> wrote:
> On Wed, 24 Jan 2018 14:21:30 +0800
> lantianyu1986@gmail.com wrote:
>
>> From: Tianyu Lan <Tianyu.Lan@microsoft.com>
>>
>> The "next" variable is redundant in hv_get_next_write_location().
>> This patch is to remove it and return write_index directly.
>>
>> Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
>> ---
>>  drivers/hv/ring_buffer.c | 4 +---
>>  1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
>> index 12eb8ca..71558e7 100644
>> --- a/drivers/hv/ring_buffer.c
>> +++ b/drivers/hv/ring_buffer.c
>> @@ -82,9 +82,7 @@ static void hv_signal_on_write(u32 old_write, struct vmbus_channel *channel)
>>  static inline u32
>>  hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
>>  {
>> -     u32 next = ring_info->ring_buffer->write_index;
>> -
>> -     return next;
>> +     return ring_info->ring_buffer->write_index;
>>  }
>>
>>  /* Set the next write location for the specified ring buffer. */
>
> Looks good.
> But let's go farther since function is only used in one location in the file
> just eliminate it completely and do simple variable references.
>
> The get/set functions in this file are unnecessary.

Yes, agree and will update patch.

>
> Better still it is possible to replace the lock based ring structure
> with a compare-exchange solution.

There are several read/write operations of ring structure in the
hv_ringbuffer_write()
and these operations should be under protection. Especially for
ring_buffer->write_index,
we need to read it to calculate available write buffer, determine
write position and then update it after
writing buffer. This sequence should be under protection, right?

-- 
Best regards
Tianyu Lan
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