Backport for .32 stable attached. Cheers,
Will. On 30 May 2011 04:44, Greg KH <[email protected]> wrote: > On Sat, May 21, 2011 at 03:25:22PM +0100, Will Tisdale wrote: >> The issue affects .32-.37 inclusive, so all of those and .35 longterm if >> possible also. >> I was surprised it hadnt already been submitted to stable. > > It didn't apply to the .32-stable tree, so if you want it there, can you > please provide a backport of it? > > I have queued it up for .33-stable now. > > thanks, > > greg k-h >
From be243fdab859a5e0cdd37f500ea233c0fd04ce73 Mon Sep 17 00:00:00 2001 From: Kasper Pedersen <[email protected]> Date: Wed, 20 Oct 2010 15:55:15 -0700 Subject: [PATCH] time: Compensate for rounding on odd-frequency clocksources upstream commit: a386b5af8edda1c742ce9f77891e112eefffc005 When the clocksource is not a multiple of HZ, the clock will be off. For acpi_pm, HZ=1000 the error is 127.111 ppm: The rounding of cycle_interval ends up generating a false error term in ntp_error accumulation since xtime_interval is not exactly 1/HZ. So, we subtract out the error caused by the rounding. This has been visible since 2.6.32-rc2 commit a092ff0f90cae22b2ac8028ecd2c6f6c1a9e4601 time: Implement logarithmic time accumulation That commit raised NTP_INTERVAL_FREQ and exposed the rounding error. testing tool: http://n1.taur.dk/permanent/testpmt.c Also tested with ntpd and a frequency counter. Signed-off-by: Kasper Pedersen <[email protected]> Acked-by: john stultz <[email protected]> Cc: John Kacur <[email protected]> Cc: Clark Williams <[email protected]> Cc: Martin Schwidefsky <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Thomas Gleixner <[email protected]> Signed-off-by: Will Tisdale <[email protected]> --- kernel/time/timekeeping.c | 9 +++++++-- 1 files changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index f5e362f..1d1206a 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -32,6 +32,8 @@ struct timekeeper { cycle_t cycle_interval; /* Number of clock shifted nano seconds in one NTP interval. */ u64 xtime_interval; + /* shifted nano seconds left over when rounding cycle_interval */ + s64 xtime_remainder; /* Raw nano seconds accumulated per NTP interval. */ u32 raw_interval; @@ -62,7 +64,7 @@ struct timekeeper timekeeper; static void timekeeper_setup_internals(struct clocksource *clock) { cycle_t interval; - u64 tmp; + u64 tmp, ntpinterval; timekeeper.clock = clock; clock->cycle_last = clock->read(clock); @@ -70,6 +72,7 @@ static void timekeeper_setup_internals(struct clocksource *clock) /* Do the ns -> cycle conversion first, using original mult */ tmp = NTP_INTERVAL_LENGTH; tmp <<= clock->shift; + ntpinterval = tmp; tmp += clock->mult/2; do_div(tmp, clock->mult); if (tmp == 0) @@ -80,6 +83,7 @@ static void timekeeper_setup_internals(struct clocksource *clock) /* Go back from cycles -> shifted ns */ timekeeper.xtime_interval = (u64) interval * clock->mult; + timekeeper.xtime_remainder = ntpinterval - timekeeper.xtime_interval; timekeeper.raw_interval = ((u64) interval * clock->mult) >> clock->shift; @@ -788,7 +792,8 @@ void update_wall_time(void) /* accumulate error between NTP and clock interval */ timekeeper.ntp_error += tick_length; - timekeeper.ntp_error -= timekeeper.xtime_interval << + timekeeper.ntp_error -= + (timekeeper.xtime_interval + timekeeper.xtime_remainder) << timekeeper.ntp_error_shift; } -- 1.7.5.2
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