On Mon, 17 Jan 2005, Roland McGrath wrote:
Shouldn't msecs mean msecs, not secs/HZ?
Hmm, sure, but why go through "msecs" at all?
--- linux-2.6/include/asm-generic/cputime.h +++ linux-2.6/include/asm-generic/cputime.h @@ -35,8 +35,8 @@ typedef u64 cputime64_t; /* * Convert cputime to seconds and back. */ -#define cputime_to_secs(__ct) (jiffies_to_msecs(__ct) / HZ) -#define secs_to_cputime(__secs) (msecs_to_jiffies(__secs * HZ)) +#define cputime_to_secs(__ct) (jiffies_to_msecs(__ct) / 1000) +#define secs_to_cputime(__secs) (msecs_to_jiffies(__secs * 1000))
iow, why not
#define cputime_to_secs(jif) ((jif) / HZ) #define secs_to_cputime(sec) ((sec) * HZ)
which avoids double rounding issues etc.
If we care, the jiffies_to_msecs() code is in include/linux/jiffies.h just prior to other conversion code that does NOT make the assumtion that HZ is exact. To be exact:
static inline long cputime_to_secs(unsigned long jif)
{
int t;
u64 result = (u64)jif * TICK_NSEC;
t = do_div(result ,NSEC_PER_SEC);
return (u32)result + t ? 1:0; /* round up if not exact */
}
#define secs_to_cputime(sec) (((U64) sec * SEC_CONVERSION) >> SEC_JIFFIE_SC)This last assumes sec worth of jiffies will actually fit in a long...
-- George Anzinger george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/
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