Messages in this thread Patch in this message | | | Date | Sat, 26 Aug 2017 07:10:39 -0700 | From | tip-bot for John Stultz <> | Subject | [tip:timers/urgent] time: Fix ktime_get_raw() incorrect base accumulation |
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Commit-ID: 0bcdc0987cce9880436b70836c6a92bb8e744fd1 Gitweb: http://git.kernel.org/tip/0bcdc0987cce9880436b70836c6a92bb8e744fd1 Author: John Stultz <john.stultz@linaro.org> AuthorDate: Fri, 25 Aug 2017 15:57:04 -0700 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Sat, 26 Aug 2017 16:06:12 +0200
time: Fix ktime_get_raw() incorrect base accumulation
In comqit fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time handling"), the following code got mistakenly added to the update of the raw timekeeper:
/* 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.
But the read function adds the shifted down tk->tkr_raw.xtime_nsec value another time, 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.
The change tried to match the monotonic base update logic:
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.
To fix this, 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.
Fixes: fc6eead7c1e2 ("time: Clean up CLOCK_MONOTONIC_RAW time handling") Reported-and-tested-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: Prarit Bhargava <prarit@redhat.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Richard Cochran <richardcochran@gmail.com> Cc: Stephen Boyd <stephen.boyd@linaro.org> Cc: Will Deacon <will.deacon@arm.com> Cc: Miroslav Lichvar <mlichvar@redhat.com> Cc: Daniel Mentz <danielmentz@google.com> Link: http://lkml.kernel.org/r/1503701824-1645-1-git-send-email-john.stultz@linaro.org
--- kernel/time/timekeeping.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
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 */
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