| Message ID | 1503701824-1645-1-git-send-email-john.stultz@linaro.org |
|---|---|
| State | Accepted |
| Commit | 0bcdc0987cce9880436b70836c6a92bb8e744fd1 |
| Headers | show |
| Series | [RFC] time: Fix ktime_get_raw() issues caused by incorrect base accumulation | expand |
Quoting John Stultz (2017-08-25 23:57:04) > In commit fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time > handling"), I mistakenly added the following: > > /* Update the monotonic raw base */ > seconds = tk->raw_sec; > nsec = (u32)(tk->tkr_raw.xtime_nsec >> tk->tkr_raw.shift); > tk->tkr_raw.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec); > > Which adds the raw_sec value and the shifted down raw xtime_nsec > to the base value. > > This is problematic as when calling ktime_get_raw(), we add the > tk->tkr_raw.xtime_nsec and current offset, shift it down and add > it to the raw base. > > This results in the shifted down tk->tkr_raw.xtime_nsec being > added twice. > > My mistake, was that I was matching the monotonic base logic > above: > > seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); > nsec = (u32) tk->wall_to_monotonic.tv_nsec; > tk->tkr_mono.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec); > > Which adds the wall_to_monotonic.tv_nsec value, but not the > tk->tkr_mono.xtime_nsec value to the base. > > The result of this is that ktime_get_raw() users (which are all > internal users) see the raw time move faster then it should > (the rate at which can vary with the current size of > tkr_raw.xtime_nsec), which has resulted in at least problems > with graphics rendering performance. > > To fix this, we simplify the tkr_raw.base accumulation to only > accumulate the raw_sec portion, and do not include the > tkr_raw.xtime_nsec portion, which will be added at read time. This fixes our testcase of using ktime_get_raw() deltas. Thanks, Tested-by: Chris Wilson <chris@chris-wilson.co.uk> -Chris
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index cedafa0..7e7e61c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -637,9 +637,7 @@ static inline void tk_update_ktime_data(struct timekeeper *tk) tk->ktime_sec = seconds; /* Update the monotonic raw base */ - seconds = tk->raw_sec; - nsec = (u32)(tk->tkr_raw.xtime_nsec >> tk->tkr_raw.shift); - tk->tkr_raw.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec); + tk->tkr_raw.base = ns_to_ktime(tk->raw_sec * NSEC_PER_SEC); } /* must hold timekeeper_lock */
In commit fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time handling"), I mistakenly added the following: /* Update the monotonic raw base */ seconds = tk->raw_sec; nsec = (u32)(tk->tkr_raw.xtime_nsec >> tk->tkr_raw.shift); tk->tkr_raw.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec); Which adds the raw_sec value and the shifted down raw xtime_nsec to the base value. This is problematic as when calling ktime_get_raw(), we add the tk->tkr_raw.xtime_nsec and current offset, shift it down and add it to the raw base. This results in the shifted down tk->tkr_raw.xtime_nsec being added twice. My mistake, was that I was matching the monotonic base logic above: seconds = (u64)(tk->xtime_sec + tk->wall_to_monotonic.tv_sec); nsec = (u32) tk->wall_to_monotonic.tv_nsec; tk->tkr_mono.base = ns_to_ktime(seconds * NSEC_PER_SEC + nsec); Which adds the wall_to_monotonic.tv_nsec value, but not the tk->tkr_mono.xtime_nsec value to the base. The result of this is that ktime_get_raw() users (which are all internal users) see the raw time move faster then it should (the rate at which can vary with the current size of tkr_raw.xtime_nsec), which has resulted in at least problems with graphics rendering performance. To fix this, we simplify the tkr_raw.base accumulation to only accumulate the raw_sec portion, and do not include the tkr_raw.xtime_nsec portion, which will be added at read time. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Miroslav Lichvar <mlichvar@redhat.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Stephen Boyd <stephen.boyd@linaro.org> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Daniel Mentz <danielmentz@google.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reported-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: John Stultz <john.stultz@linaro.org> --- kernel/time/timekeeping.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) -- 2.7.4