Messages in this thread | | | Date | Tue, 12 Nov 2002 15:46:09 +0100 (CET) | From | Tim Schmielau <> | Subject | Re: [PATCH] use 64 bit jiffies 1/4 |
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On Mon, 11 Nov 2002, Linus Torvalds wrote:
> I disagree with the implementation of this (and yes, I would also prefer > for it to be called "jiffies64_to_clock_t()"):
I'm fine with the name "jiffies_64_to_clock_t()". I'd like "jiffies64_to_clock_t()" (without the first underscore) even more, but this is inconsistent with jiffies_64. (And I don't know if we want to rename the latter now)
> This is wrong. You should really start off by fixing the 32-bit case, > since even that needs fixing anyway (some interfaces really _are_ > 32-bit, and cannot be expanded). > > It also only works for cases where HZ is a direct multiple of USER_HZ, > and yes, my original code has the same problem, but that's not a good > excuse to make it worse. I think it should be fairly straightforward to > get this right, and have a simple
OK, changed my patch to
+#if (HZ % USER_HZ)==0 # define jiffies_to_clock_t(x) ((x) / (HZ / USER_HZ)) +#else +# define jiffies_to_clock_t(x) ((clock_t) jiffies_64_to_clock_t((u64) x)) +#endif + +static inline u64 jiffies_64_to_clock_t(u64 x) +{ +#if (HZ % USER_HZ)==0 + do_div(x, HZ / USER_HZ); +#else + /* + * There are better ways that don't overflow early, + * but even this doesn't overflow in hundreds of years + * in 64 bits, so.. + */ + x *= USER_HZ; + do_div(x, HZ); +#endif + return x; +}
I'll send the full new set of patches off-list. They can also be retrieved from http://www.physik3.uni-rostock.de/tim/kernel/2.5/jiffies64-32a.patch.gz (1/4: infrastructure) http://www.physik3.uni-rostock.de/tim/kernel/2.5/jiffies64-32b.patch.gz (2/4: fix uptime wrap) http://www.physik3.uni-rostock.de/tim/kernel/2.5/jiffies64-32c.patch.gz (3/4: 64 bit process start time) http://www.physik3.uni-rostock.de/tim/kernel/2.5/jiffies64-32d.patch.gz (4/4: use unsigned long for cpu statistics)
> (And yes, the above does not return a clock_t, it returns a 64-bit > thing, but people who need to can truncate it to clock_t and live with > the old 497-day overflow of USER_HZ in 32 bits for broken interfaces > like "clock()". This way the caller can use the same function for both > the "true 64-bit result" and the truncated case).
Hey, this is just why I renamed it from "jiffies_64_to_clock_t()" to "jiffies_64_to_user_HZ()" before sending it off :-)
> And then we should just remove the "jiffies_to_clock_t()" thing, I > suspect. The 49-day overflow is just too soon for comfort, you're > definitely right about that.
OK, will prepare patch for that later.
Tim
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