Re: [RFC][PATCH 1/4] add jiffies_to_nsecs() helper and fix up size of usecs

[Nishanth Aravamudan <nacc@us.ibm.com>]

On 15.07.2005 [14:14:25 +0200], Pavel Machek wrote:
> Hi!
> 
> > > > +static inline u64 jiffies_to_nsecs(const unsigned long j)
> > > > +{
> > > > +#if HZ <= NSEC_PER_SEC && !(NSEC_PER_SEC % HZ)
> > > > +	return (NSEC_PER_SEC / HZ) * (u64)j;
> > > > +#elif HZ > NSEC_PER_SEC && !(HZ % NSEC_PER_SEC)
> > > > +	return ((u64)j + (HZ / NSEC_PER_SEC) - 1)/(HZ / NSEC_PER_SEC);
> > > > +#else
> > > > +	return ((u64)j * NSEC_PER_SEC) / HZ;
> > > > +#endif
> > > > +}
> > > 
> > > That might look a little better something like:
> > > 
> > > static inline u64 jiffies_to_nsecs(const unsigned long __j)
> > > {
> > > 	u64 j = __j;
> > > 
> > > 	if (HZ <= NSEC_PER_SEC && !(NSEC_PER_SEC % HZ))
> > > 		return (NSEC_PER_SEC / HZ) * j;
> > > 	else if (HZ > NSEC_PER_SEC && !(HZ % NSEC_PER_SEC))
> > > 		return (j + (HZ / NSEC_PER_SEC) - 1)/(HZ / NSEC_PER_SEC);
> > > 	else
> > > 		return (j * NSEC_PER_SEC) / HZ;
> > > }
> > > 
> > > Compilers are smart :)
> > 
> > Well, I was trying to keep it similar to the other conversion functions.
> > I guess the compiler can evaluate the conditional full of constants at
> > compile-time regardless of whether it is #if or if ().
> > 
> > I can make these changes if others would like them as well.
> 
> Yes, please. And feel free to convert nearby functions, too ;-).

I have a patch to make this change for all the jiffies <--> human-time
functions, but have a problem. I noticed that these functions, in the
if/else form (as opposed to #if/#else) will warn about division-by-zero
problems, as (HZ / MSEC_PER_SEC), (HZ / USEC_PER_SEC) & (HZ /
NSEC_PER_SEC) are all 0 if HZ < 1000 (which, of course, is the default
now :) ). Any suggestions? Just leave the functions as is? Even then,
I'm going to update this patch to use USEC_PER_SEC and MSEC_PER_SEC in
the other conversion functions like I use NSEC_PER_SEC in the first
version.

Thanks,
Nish