number of elements or bytes for kfifo_in etc

number of elements or bytes for kfifo_in etc

[Huang Ying]

Hi, Stefani,

In new kfifo implementation in 2.6.36-rc1, description of the third
parameter is:

"@n: number of elements to be added"

But if my understanding is correct, the actual implementation is:

"@n: number of bytes to be added"

That is sizeof(*fifo->type) is not considered.

I think we should change either the implementation or the description.

Best Regards,
Huang Ying

Re: number of elements or bytes for kfifo_in etc

[Stefani Seibold]

Am Mittwoch, den 18.08.2010, 13:29 +0800 schrieb Huang Ying:
> Hi, Stefani,
> 
> In new kfifo implementation in 2.6.36-rc1, description of the third
> parameter is:
> 
> "@n: number of elements to be added"
> 
> But if my understanding is correct, the actual implementation is:
> 
> "@n: number of bytes to be added"
> 

Number of bytes is wrong, this is only valid for byte stream fifo's
where an element is a byte.

Have a look at samples/kfifo/inttype-example.c where an element is a int
type.

Re: number of elements or bytes for kfifo_in etc

[Huang Ying]

Hi, Stefani,

On Thu, 2010-08-19 at 00:35 +0800, Stefani Seibold wrote:
> Am Mittwoch, den 18.08.2010, 13:29 +0800 schrieb Huang Ying:
> > Hi, Stefani,
> > 
> > In new kfifo implementation in 2.6.36-rc1, description of the third
> > parameter is:
> > 
> > "@n: number of elements to be added"
> > 
> > But if my understanding is correct, the actual implementation is:
> > 
> > "@n: number of bytes to be added"
> > 
> 
> Number of bytes is wrong, this is only valid for byte stream fifo's
> where an element is a byte.
> 
> Have a look at samples/kfifo/inttype-example.c where an element is a int
> type.

Yes. You are right. I misunderstood your code. Sorry for bothering.

Best Regards,
Huang Ying

Re: number of elements or bytes for kfifo_in etc

[Huang Ying]

On Thu, 2010-08-19 at 08:32 +0800, Huang Ying wrote:
> Hi, Stefani,
> 
> On Thu, 2010-08-19 at 00:35 +0800, Stefani Seibold wrote:
> > Am Mittwoch, den 18.08.2010, 13:29 +0800 schrieb Huang Ying:
> > > Hi, Stefani,
> > > 
> > > In new kfifo implementation in 2.6.36-rc1, description of the third
> > > parameter is:
> > > 
> > > "@n: number of elements to be added"
> > > 
> > > But if my understanding is correct, the actual implementation is:
> > > 
> > > "@n: number of bytes to be added"
> > > 
> > 
> > Number of bytes is wrong, this is only valid for byte stream fifo's
> > where an element is a byte.
> > 
> > Have a look at samples/kfifo/inttype-example.c where an element is a int
> > type.
> 
> Yes. You are right. I misunderstood your code. Sorry for bothering.

And I found __kfifo->esize is used in __kfifo_in/out etc to convert
between elements and bytes. Maybe we can pull the conversion code to
corresponding macro, because where esize is constant and may be
optimized to bit shifting or nothing. What do you think about that?

Best Regards,
Huang Ying

Re: number of elements or bytes for kfifo_in etc

[Stefani Seibold]

Am Donnerstag, den 19.08.2010, 09:15 +0800 schrieb Huang Ying:
> On Thu, 2010-08-19 at 08:32 +0800, Huang Ying wrote:
> > Hi, Stefani,
> > 
> > On Thu, 2010-08-19 at 00:35 +0800, Stefani Seibold wrote:
> > > Am Mittwoch, den 18.08.2010, 13:29 +0800 schrieb Huang Ying:
> > > > Hi, Stefani,
> > > > 
> > > > In new kfifo implementation in 2.6.36-rc1, description of the third
> > > > parameter is:
> > > > 
> > > > "@n: number of elements to be added"
> > > > 
> > > > But if my understanding is correct, the actual implementation is:
> > > > 
> > > > "@n: number of bytes to be added"
> > > > 
> > > 
> > > Number of bytes is wrong, this is only valid for byte stream fifo's
> > > where an element is a byte.
> > > 
> > > Have a look at samples/kfifo/inttype-example.c where an element is a int
> > > type.
> > 
> > Yes. You are right. I misunderstood your code. Sorry for bothering.
> 
> And I found __kfifo->esize is used in __kfifo_in/out etc to convert
> between elements and bytes. Maybe we can pull the conversion code to
> corresponding macro, because where esize is constant and may be
> optimized to bit shifting or nothing. What do you think about that?
> 

esize isn't constant, especially from the point of view inside
__kfifo_in and so on. The is ony good reason not to pass the size of the
element using sizeof(*fifo->type) as a parameter, it will generate more
code. Storing the size of the element in the kfifo structure is the
better decision.

But if you found a better way and can prove it under any circumstance
with a list of measurement results u will get an ack!

- Stefani