Re: [PATCH 5/5] scsi_debug: Implement support for DIF Type 2

[Boaz Harrosh <bharrosh@panasas.com>]

On 08/27/2009 05:30 PM, James Bottomley wrote:
> On Thu, 2009-08-27 at 17:20 +0300, Boaz Harrosh wrote:
>> On 08/27/2009 04:41 PM, James Bottomley wrote:
>>>
>>> The general rule is not to confuse coding styles, so the correct way to
>>> add stuff is to use the existing conventions in the file.  You can
>>> optionally convert the entire style if necessary.  However, for these
>>> get_cpu_be macros, there's no real benefit other than saving typing, so
>>> a global conversion effort simply isn't worth it.
>>>
>>
>> This is not right. The get_cpu_be macros are ten fold faster and smaller
>> on all the platforms we ever use. I'm talking about 16-96 to 1 for a 64 bit
>> operation.
> 
> Assembly comparisons didn't bear this out the last time I looked; what
> changed?
> 

I'm not sure what test you made. But for instance on x86_64 which has unaligned
cpu support, the get_unaligned_be64 is a simple SWAB instructions as opposed to
8 "or" + 8 "shift". Not to mention BE systems which do nothing (memcpy)

>> Not to mention the heart attack it gives me every time. Is that index go down
>> or up? the shifts go bigger or smaller? even just for that I would wrap them,
>> triple check, and never use anything else. But the stronger fact of the matter
>> is that I don't think there is a single used ARCH that does shifts anymore.
> 
> OK, but for those of us who read the standards, they explicitly specify
> byte offset fields for everything, so cmnd[n] does map exactly to that,
> so I find the fully folded out form easier to read and compare with the
> relevant standard text.
> 
> That's why I'm not mandating anything other than keep the styles
> consistent per file.  You're free to use whatever you like in your
> files.
> 
> James
> 
> 

Boaz