2.6.32-longterm review patch. If anyone has any objections, please let me know.
------------------ 61b76840ddee647c0c223365378c3f394355b7d7 From: John Stultz <[email protected]> Commit 61b76840ddee647c0c223365378c3f394355b7d7 ("time: Avoid making adjustments if we haven't accumulated anything") introduced a regression with nohz. Basically with kernels between 2.6.20-something to 2.6.32, we accumulate time in half second chunks, rather then every timer-tick. This was added because when NOHZ landed, if you were idle for a few seconds, you had to spin for every tick we skipped in the accumulation loop, which created some bad latencies. However, this required that we create the xtime_cache() which was still updated each tick, so that filesystem timestamps, etc continued to see time increment normally. Of course, the xtime_cache is updated at the bottom of update_wall_time(). So the early return on (offset < timekeeper.cycle_interval), added by the problematic commit causes the xtime_cache to not be updated. This can cause code using current_kernel_time() (like the mqueue code) or hrtimer_get_softirq_time(), which uses the non-updated xtime_cache, to see timers to fire with very coarse half-second granularity. Many thanks to Romain for describing the issue clearly, providing test case to reproduce it and helping with testing the solution. This change is for 2.6.32-stable ONLY! Cc: [email protected] Cc: Willy Tarreau <[email protected]> Cc: Romain Francoise <[email protected]> Reported-by: Romain Francoise <[email protected]> Tested-by: Romain Francoise <[email protected]> Signed-off-by: John Stultz <[email protected]> Signed-off-by: Willy Tarreau <[email protected]> --- kernel/time/timekeeping.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 3d35af3..f65a0fb 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -809,7 +809,7 @@ void update_wall_time(void) #endif /* Check if there's really nothing to do */ if (offset < timekeeper.cycle_interval) - return; + goto out; timekeeper.xtime_nsec = (s64)xtime.tv_nsec << timekeeper.shift; @@ -881,6 +881,7 @@ void update_wall_time(void) timekeeper.ntp_error += timekeeper.xtime_nsec << timekeeper.ntp_error_shift; +out: nsecs = clocksource_cyc2ns(offset, timekeeper.mult, timekeeper.shift); update_xtime_cache(nsecs); -- 1.7.12.2.21.g234cd45.dirty -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
