Messages in this thread Patch in this message |  | | | From | John Stultz <> | | Subject | [PATCH 4/9] time: Update timekeeper structure using a local shadow | | Date | Thu, 1 Mar 2012 23:12:43 -0800 |
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Uses a local shadow structure to update the timekeeper. This will allow for reduced timekeeper.rlock hold time.
CC: Ingo Molnar <mingo@elte.hu> CC: Thomas Gleixner <tglx@linutronix.de> CC: Eric Dumazet <eric.dumazet@gmail.com> CC: Richard Cochran <richardcochran@gmail.com> Signed-off-by: John Stultz <john.stultz@linaro.org> --- kernel/time/timekeeping.c | 43 +++++++++++++++++++++++-------------------- 1 files changed, 23 insertions(+), 20 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index f9ee96c..09460c1 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -74,6 +74,7 @@ struct timekeeper { }; static struct timekeeper timekeeper; +static struct timekeeper shadow_tk; /* Locks for timekeeper variable: */ /* This seqcount serializes readers from updates */ @@ -1072,10 +1073,11 @@ static void update_wall_time(void) if (unlikely(timekeeping_suspended)) goto out; - clock = timekeeper.clock; + shadow_tk = timekeeper; + clock = shadow_tk.clock; #ifdef CONFIG_ARCH_USES_GETTIMEOFFSET - offset = timekeeper.cycle_interval; + offset = shadow_tk.cycle_interval; #else offset = (clock->read(clock) - clock->cycle_last) & clock->mask; #endif @@ -1088,19 +1090,19 @@ static void update_wall_time(void) * chunk in one go, and then try to consume the next smaller * doubled multiple. */ - shift = ilog2(offset) - ilog2(timekeeper.cycle_interval); + shift = ilog2(offset) - ilog2(shadow_tk.cycle_interval); shift = max(0, shift); /* Bound shift to one less then what overflows tick_length */ maxshift = (64 - (ilog2(ntp_tick_length())+1)) - 1; shift = min(shift, maxshift); - while (offset >= timekeeper.cycle_interval) { - offset = logarithmic_accumulation(&timekeeper, offset, shift); - if(offset < timekeeper.cycle_interval<<shift) + while (offset >= shadow_tk.cycle_interval) { + offset = logarithmic_accumulation(&shadow_tk, offset, shift); + if (offset < shadow_tk.cycle_interval<<shift) shift--; } /* correct the clock when NTP error is too big */ - timekeeping_adjust(&timekeeper, offset); + timekeeping_adjust(&shadow_tk, offset); /* * Since in the loop above, we accumulate any amount of time @@ -1118,10 +1120,10 @@ static void update_wall_time(void) * We'll correct this error next time through this function, when * xtime_nsec is not as small. */ - if (unlikely((s64)timekeeper.xtime_nsec < 0)) { - s64 neg = -(s64)timekeeper.xtime_nsec; - timekeeper.xtime_nsec = 0; - timekeeper.ntp_error += neg << timekeeper.ntp_error_shift; + if (unlikely((s64)shadow_tk.xtime_nsec < 0)) { + s64 neg = -(s64)shadow_tk.xtime_nsec; + shadow_tk.xtime_nsec = 0; + shadow_tk.ntp_error += neg << shadow_tk.ntp_error_shift; } /* @@ -1133,23 +1135,24 @@ static void update_wall_time(void) * the vsyscall implementations are converted to use xtime_nsec * (shifted nanoseconds), this can be killed. */ - remainder = timekeeper.xtime_nsec & ((1<<timekeeper.shift)-1); - timekeeper.xtime_nsec -= remainder; - timekeeper.xtime_nsec += 1<<timekeeper.shift; - timekeeper.ntp_error += remainder << - timekeeper.ntp_error_shift; + remainder = shadow_tk.xtime_nsec & ((1<<shadow_tk.shift)-1); + shadow_tk.xtime_nsec -= remainder; + shadow_tk.xtime_nsec += 1<<shadow_tk.shift; + shadow_tk.ntp_error += remainder << shadow_tk.ntp_error_shift; /* * Finally, make sure that after the rounding * xtime.tv_nsec isn't larger then NSEC_PER_SEC */ - if (unlikely(timekeeper.xtime_nsec >= - ((u64)NSEC_PER_SEC << timekeeper.shift))) { - timekeeper.xtime_nsec -= (u64)NSEC_PER_SEC << timekeeper.shift; - timekeeper.xtime_sec++; + if (unlikely(shadow_tk.xtime_nsec >= + ((u64)NSEC_PER_SEC << shadow_tk.shift))) { + shadow_tk.xtime_nsec -= (u64)NSEC_PER_SEC << shadow_tk.shift; + shadow_tk.xtime_sec++; second_overflow(); } + + timekeeper = shadow_tk; timekeeping_update(&timekeeper, false); out: -- 1.7.3.2.146.gca209
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