Re: do_div64 generic

[george anzinger <george@mvista.com>]

Andrew Morton wrote:
> george anzinger <george@mvista.com> wrote:
> 
>>>George, do you agree? May I go on and post a patch killing
>>>div_long_long_rem() everywhere?
>>
>>The issue is that div is a very long instruction and the do_div() 
>>thing uses 2 or three of them, while the div_long_long_rem() is just 
>>1.  Also, a lot of archs already have the required div by a different 
>>name.  It all boils down to a performance thing.
> 
> 
> It is only used in nanosleep(), and then only in the case where the sleep
> terminated early.
> 
> If someone is calling nanosleep() so frequently for this to matter, the
> time spent in divide is the least of their problems.  Unless you have some
> real-worldish benchmarks to demonstrate otherwise?

It is also used in the jiffies to timespec and jiffies to timeval code 
in timer.h, if memory serves.
> 
> You know what they say about premtur optmstns, and having to propagate
> funky new divide primitives across N architectures is indeed evil.

Hm.  I only want the simple div.  64-bit/32-bit in two 32-bit results. 
  Is this funky?  And the "evil" #ifdef allows archs to not do it.
> 
> Bernardo, can you do the patch please?
> 
> 

-- 
George Anzinger   george@mvista.com
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml