Due to how the MONOTONIC_RAW accumulation logic was handled,
there is the potential for a 1ns discontinuity when we do
accumulations. This small discontinuity has for the most part
gone un-noticed, but since ARM64 enabled CLOCK_MONOTONIC_RAW
in their vDSO clock_gettime implementation, we've seen failures
with the inconsistency-check test in kselftest.
This patch addresses the issue by using the same sub-ns
accumulation handling that CLOCK_MONOTONIC uses, which avoids
the issue for in-kernel users.
Since the ARM64 vDSO implementation has its own clock_gettime
calculation logic, this patch reduces the frequency of errors,
but failures are still seen. The ARM64 vDSO will need to be
updated to include the sub-nanosecond xtime_nsec values in its
calculation for this issue to be completely fixed.
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Miroslav Lichvar <mlich...@redhat.com>
Cc: Richard Cochran <richardcoch...@gmail.com>
Cc: Prarit Bhargava <pra...@redhat.com>
Cc: Stephen Boyd <stephen.b...@linaro.org>
Cc: Kevin Brodsky <kevin.brod...@arm.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Daniel Mentz <danielme...@google.com>
Signed-off-by: John Stultz <john.stu...@linaro.org>
---
include/linux/timekeeper_internal.h | 4 ++--
kernel/time/timekeeping.c | 21 ++++++++++++---------
2 files changed, 14 insertions(+), 11 deletions(-)
diff --git a/include/linux/timekeeper_internal.h
b/include/linux/timekeeper_internal.h
index 110f453..528cc86 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -58,7 +58,7 @@ struct tk_read_base {
* interval.
* @xtime_remainder: Shifted nano seconds left over when rounding
* @cycle_interval
- * @raw_interval: Raw nano seconds accumulated per NTP interval.
+ * @raw_interval: Shifted raw nano seconds accumulated per NTP interval.
* @ntp_error: Difference between accumulated time and NTP time in ntp
* shifted nano seconds.
* @ntp_error_shift: Shift conversion between clock shifted nano seconds and
@@ -100,7 +100,7 @@ struct timekeeper {
u64 cycle_interval;
u64 xtime_interval;
s64 xtime_remainder;
- u32 raw_interval;
+ u64 raw_interval;
/* The ntp_tick_length() value currently being used.
* This cached copy ensures we consistently apply the tick
* length for an entire tick, as ntp_tick_length may change
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index abc1968..35d3ba3 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -282,7 +282,7 @@ static void tk_setup_internals(struct timekeeper *tk,
struct clocksource *clock)
/* Go back from cycles -> shifted ns */
tk->xtime_interval = interval * clock->mult;
tk->xtime_remainder = ntpinterval - tk->xtime_interval;
- tk->raw_interval = (interval * clock->mult) >> clock->shift;
+ tk->raw_interval = interval * clock->mult;
/* if changing clocks, convert xtime_nsec shift units */
if (old_clock) {
@@ -1994,7 +1994,7 @@ static u64 logarithmic_accumulation(struct timekeeper
*tk, u64 offset,
u32 shift, unsigned int *clock_set)
{
u64 interval = tk->cycle_interval << shift;
- u64 raw_nsecs;
+ u64 nsecps;
/* If the offset is smaller than a shifted interval, do nothing */
if (offset < interval)
@@ -2009,14 +2009,17 @@ static u64 logarithmic_accumulation(struct timekeeper
*tk, u64 offset,
*clock_set |= accumulate_nsecs_to_secs(tk);
/* Accumulate raw time */
- raw_nsecs = (u64)tk->raw_interval << shift;
- raw_nsecs += tk->raw_time.tv_nsec;
- if (raw_nsecs >= NSEC_PER_SEC) {
- u64 raw_secs = raw_nsecs;
- raw_nsecs = do_div(raw_secs, NSEC_PER_SEC);
- tk->raw_time.tv_sec += raw_secs;
+ tk->tkr_raw.xtime_nsec += (u64)tk->raw_time.tv_nsec
+ << tk->tkr_raw.shift;
+ tk->tkr_raw.xtime_nsec += tk->raw_interval << shift;
+ nsecps = (u64)NSEC_PER_SEC << tk->tkr_raw.shift;
+ while (tk->tkr_raw.xtime_nsec >= nsecps) {
+ tk->tkr_raw.xtime_nsec -= nsecps;
+ tk->raw_time.tv_sec++;
}
- tk->raw_time.tv_nsec = raw_nsecs;
+ tk->raw_time.tv_nsec = tk->tkr_raw.xtime_nsec >> tk->tkr_raw.shift;
+ tk->tkr_raw.xtime_nsec -= (u64)tk->raw_time.tv_nsec
+ << tk->tkr_raw.shift;
/* Accumulate error between NTP and clock interval */
tk->ntp_error += tk->ntp_tick << shift;
--
2.7.4
