Re: [RFC][PATCH] new timeofday core subsystem (v. A3)

[Christoph Lameter]

On Fri, 11 Mar 2005, john stultz wrote:

> +/* cyc2ns():
> + *		Uses the timesource and ntp ajdustment interval to
> + *		convert cycle_ts to nanoseconds.
> + *		If rem is not null, it stores the remainder of the
> + *		calculation there.
> + *
> + */

This function is called in critical paths and it would be very important
to optimize it further.

> +static inline nsec_t cyc2ns(struct timesource_t* ts, int ntp_adj, cycle_t cycles, cycle_t* rem)
> +{
> +	u64 ret;
> +	ret = (u64)cycles;
> +	ret *= (ts->mult + ntp_adj);

This only changes when nt_adj changes. Maybe maintain the sum separately?

> +	if (unlikely(rem)) {
> +		/* XXX clean this up later!
> +		 *		buf for now relax, we only calc
> +		 *		remainders at interrupt time
> +		 */
> +		u64 remainder = ret & ((1 << ts->shift) -1);
> +		do_div(remainder, ts->mult);
> +		*rem = remainder;

IA64 does not do remainder processing (maybe I just do not understand
this...) but this seems to be not necessay if one uses 64 bit values that
are properly shifted?

> +	}
> +	ret >>= ts->shift;
> +	return (nsec_t)ret;
> +}

The whole function could simply be:

#define cyc2ns(cycles, ts) (cycles*ts->current_factor) >> ts->shift
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/