linux-kernel - Re: [Patch] vmbus: Simply hv_get_next_write

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Message-ID: <CAOLK0pzyd-XZkbOmDwN=JvGNDd7zRzL=BBoCzW70hAXWcdF9Ag@mail.gmail.com>
Date:   Thu, 25 Jan 2018 16:33:37 +0800
From:   Tianyu Lan <lantianyu1986@...il.com>
To:     Stephen Hemminger <stephen@...workplumber.org>
Cc:     sthemmin@...rosoft.com, haiyangz@...rosoft.com,
        "linux-kernel@...r kernel org" <linux-kernel@...r.kernel.org>,
        devel@...uxdriverproject.org, Tianyu Lan <Tianyu.Lan@...rosoft.com>
Subject: Re: [Patch] vmbus: Simply hv_get_next_write_location() function

On Thu, Jan 25, 2018 at 12:37 AM, Stephen Hemminger
<stephen@...workplumber.org> wrote:
> On Wed, 24 Jan 2018 14:21:30 +0800
> lantianyu1986@...il.com wrote:
>
>> From: Tianyu Lan <Tianyu.Lan@...rosoft.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@...rosoft.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