Messages in this thread Patch in this message | | | From | Chris Metcalf <> | Subject | [PATCH v2] tile: avoid using clocksource_cyc2ns with absolute cycle count | Date | Wed, 16 Nov 2016 14:35:33 -0500 |
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For large values of "mult" and long uptimes, the intermediate result of "cycles * mult" can overflow 64 bits. For example, the tile platform calls clocksource_cyc2ns with a 1.2 GHz clock; we have mult = 853, and after 208.5 days, we overflow 64 bits.
Since clocksource_cyc2ns() is intended to be used for relative cycle counts, not absolute cycle counts, performance is more importance than accepting a wider range of cycle values. So, just use mult_frac() directly in tile's sched_clock().
Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com> --- Blackfin should make a similar change in their sched_clock().
arch/tile/kernel/time.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c index 178989e6d3e3..ea960d660917 100644 --- a/arch/tile/kernel/time.c +++ b/arch/tile/kernel/time.c @@ -218,8 +218,8 @@ void do_timer_interrupt(struct pt_regs *regs, int fault_num) */ unsigned long long sched_clock(void) { - return clocksource_cyc2ns(get_cycles(), - sched_clock_mult, SCHED_CLOCK_SHIFT); + return mult_frac(get_cycles(), + sched_clock_mult, 1ULL << SCHED_CLOCK_SHIFT); } int setup_profiling_timer(unsigned int multiplier) -- 2.7.2
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