Messages in this thread | | | Date | Wed, 7 May 2014 15:38:23 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] sched/clock: cleanup, remove wrap_{max|min}(). |
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On Wed, May 07, 2014 at 09:04:19PM +0900, Dongsheng Yang wrote: > On 05/07/2014 09:55 PM, Peter Zijlstra wrote: > >On Wed, May 07, 2014 at 08:48:58PM +0900, Dongsheng Yang wrote: > >>I am not sure why we need the wrap_{max|min}() in kernel/sched/clock.c. > >>But I checked the implementation of max() and min() in linux/kernel.h, I think > >>we can reuse them here rather than introduce a new function named > >>wrap_{max|min}(). > >wrap is a good hint there.. they're supposed to deal with the clock > >wrapping. Of course 2^64 ns is a rather long time (~584 years in fact), > >but that doesn't mean we shouldn't care. > > > >And no, min/max don't do the right thing. > > IMMO, max() in kernel.h is checking and returning the u64 with typeof() if > we are passing a u64 parameter to max(). And I checked current callers of > wrap_max(), > they are all passing parameters of u64 type. So I think max/min works well > at > the place of wrap_max/min(). > > Maybe I am missing something here, please correct me if I understand it > incorrectly.
Trivial test prog; you really should do these things yourself.
$ ./wrap wrap_min: 18446744073709551615 wrap_max: 0 min: 0 max: 18446744073709551615
--- #include <stdint.h> #include <stdio.h>
typedef uint64_t u64; typedef int64_t s64;
static inline u64 wrap_min(u64 x, u64 y) { return (s64)(x - y) < 0 ? x : y; }
static inline u64 wrap_max(u64 x, u64 y) { return (s64)(x - y) > 0 ? x : y; }
#define min(x, y) ({ \ typeof(x) _min1 = (x); \ typeof(y) _min2 = (y); \ (void) (&_min1 == &_min2); \ _min1 < _min2 ? _min1 : _min2; })
#define max(x, y) ({ \ typeof(x) _max1 = (x); \ typeof(y) _max2 = (y); \ (void) (&_max1 == &_max2); \ _max1 > _max2 ? _max1 : _max2; })
void main (void) { u64 a = UINT64_MAX, b = a + 1;
printf("wrap_min: %lu wrap_max: %lu\n", wrap_min(a, b), wrap_max(a,b)); printf("min: %lu max: %lu\n", min(a, b), max(a,b)); } [unhandled content-type:application/pgp-signature] | |