Messages in this thread Patch in this message | | | From | Thomas Graziadei <> | Subject | [PATCH] timekeeping: Fix 1ns/tick drift with GENERIC_TIME_VSYSCALL_OLD | Date | Tue, 31 May 2016 15:06:06 +0200 |
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From: Thomas Graziadei <thomas.graziadei@omicronenergy.com>
The user notices the problem in a raw and real time drift, calling clock_gettime with CLOCK_REALTIME / CLOCK_MONOTONIC_RAW on a system with no ntp correction taking place (no ntpd or ptp stuff running).
The problem is, that old_vsyscall_fixup adds an extra 1ns even though xtime_nsec is already held in full nsecs and the remainder in this case is 0. Do the rounding up buisness only if needed.
Signed-off-by: Thomas Graziadei <thomas.graziadei@omicronenergy.com> --- kernel/time/timekeeping.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 479d25c..a196e08 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -480,10 +480,12 @@ static inline void old_vsyscall_fixup(struct timekeeper *tk) * users are removed, this can be killed. */ remainder = tk->tkr_mono.xtime_nsec & ((1ULL << tk->tkr_mono.shift) - 1); - tk->tkr_mono.xtime_nsec -= remainder; - tk->tkr_mono.xtime_nsec += 1ULL << tk->tkr_mono.shift; - tk->ntp_error += remainder << tk->ntp_error_shift; - tk->ntp_error -= (1ULL << tk->tkr_mono.shift) << tk->ntp_error_shift; + if (remainder != 0) { + tk->tkr_mono.xtime_nsec -= remainder; + tk->tkr_mono.xtime_nsec += 1ULL << tk->tkr_mono.shift; + tk->ntp_error += remainder << tk->ntp_error_shift; + tk->ntp_error -= (1ULL << tk->tkr_mono.shift) << tk->ntp_error_shift; + } } #else #define old_vsyscall_fixup(tk) -- 1.9.1
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