Messages in this thread |  | | | Date | Wed, 19 Jan 2005 16:18:03 -0800 | | From | George Anzinger <> | | Subject | Re: [PATCH] cputime.h seems to assume HZ==1000 |
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Linus Torvalds wrote: > > 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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