Re: [PATCH] tile: avoid overflow in ns2cycles
On 3/4/2014 3:20 AM, Henrik Austad wrote:
> In commit 4cecf6d401a ("sched, x86: Avoid unnecessary overflow in
> sched_clock") and in recent patch "clocksource: avoid unnecessary
> overflow in cyclecounter_cyc2ns()" https://lkml.org/lkml/2014/3/4/17,
> the mult-shift approach is replaced by 2 steps to avoid storing a large,
> intermediate value that could overflow.
>
> arch/tile/kernel/time.c has a similar pattern in cycles2ns, and this
> copies the same pattern in this function
>
> CC: John Stultz
> CC: Mike Galbraith
> CC: Salman Qazi
> Signed-off-by: Henrik Austad
> ---
> arch/tile/kernel/time.c | 10 +-
> 1 file changed, 9 insertions(+), 1 deletion(-)
Thanks; taken into the tile tree (with some minor whitespace formatting tweaks).
--
Chris Metcalf, Tilera Corp.
http://www.tilera.com
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Re: [PATCH] tile: avoid overflow in ns2cycles
On 3/4/2014 3:20 AM, Henrik Austad wrote: In commit 4cecf6d401a (sched, x86: Avoid unnecessary overflow in sched_clock) and in recent patch clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns() https://lkml.org/lkml/2014/3/4/17, the mult-shift approach is replaced by 2 steps to avoid storing a large, intermediate value that could overflow. arch/tile/kernel/time.c has a similar pattern in cycles2ns, and this copies the same pattern in this function CC: John Stultz johns...@us.ibm.com CC: Mike Galbraith bitbuc...@online.de CC: Salman Qazi sq...@google.com Signed-off-by: Henrik Austad hen...@austad.us --- arch/tile/kernel/time.c | 10 +- 1 file changed, 9 insertions(+), 1 deletion(-) Thanks; taken into the tile tree (with some minor whitespace formatting tweaks). -- Chris Metcalf, Tilera Corp. http://www.tilera.com -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] tile: avoid overflow in ns2cycles
In commit 4cecf6d401a ("sched, x86: Avoid unnecessary overflow in
sched_clock") and in recent patch "clocksource: avoid unnecessary
overflow in cyclecounter_cyc2ns()" https://lkml.org/lkml/2014/3/4/17,
the mult-shift approach is replaced by 2 steps to avoid storing a large,
intermediate value that could overflow.
arch/tile/kernel/time.c has a similar pattern in cycles2ns, and this
copies the same pattern in this function
CC: John Stultz
CC: Mike Galbraith
CC: Salman Qazi
Signed-off-by: Henrik Austad
---
arch/tile/kernel/time.c | 10 +-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
index 5d10642..9e74733 100644
--- a/arch/tile/kernel/time.c
+++ b/arch/tile/kernel/time.c
@@ -236,7 +236,15 @@ cycles_t ns2cycles(unsigned long nsecs)
* clock frequency.
*/
struct clock_event_device *dev = &__raw_get_cpu_var(tile_timer);
- return ((u64)nsecs * dev->mult) >> dev->shift;
+
+ /*
+* as in clocksource.h and x86's timer.h, we split the calculation into
2
+* parts to avoid unecessary overflow of the intermediate value. This
will
+* not lead to any loss of precision.
+*/
+ u64 quot = (u64)nsecs >> dev->shift;
+ u64 rem = (u64)nsecs & ((1ULL << dev->shift)-1);
+ return quot * dev->mult + ((rem * dev->mult) >> dev->shift);
}
void update_vsyscall_tz(void)
--
1.7.10.4
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[PATCH] tile: avoid overflow in ns2cycles
In commit 4cecf6d401a (sched, x86: Avoid unnecessary overflow in sched_clock) and in recent patch clocksource: avoid unnecessary overflow in cyclecounter_cyc2ns() https://lkml.org/lkml/2014/3/4/17, the mult-shift approach is replaced by 2 steps to avoid storing a large, intermediate value that could overflow. arch/tile/kernel/time.c has a similar pattern in cycles2ns, and this copies the same pattern in this function CC: John Stultz johns...@us.ibm.com CC: Mike Galbraith bitbuc...@online.de CC: Salman Qazi sq...@google.com Signed-off-by: Henrik Austad hen...@austad.us --- arch/tile/kernel/time.c | 10 +- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c index 5d10642..9e74733 100644 --- a/arch/tile/kernel/time.c +++ b/arch/tile/kernel/time.c @@ -236,7 +236,15 @@ cycles_t ns2cycles(unsigned long nsecs) * clock frequency. */ struct clock_event_device *dev = __raw_get_cpu_var(tile_timer); - return ((u64)nsecs * dev-mult) dev-shift; + + /* +* as in clocksource.h and x86's timer.h, we split the calculation into 2 +* parts to avoid unecessary overflow of the intermediate value. This will +* not lead to any loss of precision. +*/ + u64 quot = (u64)nsecs dev-shift; + u64 rem = (u64)nsecs ((1ULL dev-shift)-1); + return quot * dev-mult + ((rem * dev-mult) dev-shift); } void update_vsyscall_tz(void) -- 1.7.10.4 -- To unsubscribe from this list: send the line unsubscribe linux-kernel in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
