diff options
author | Thomas Gleixner <tglx@linutronix.de> | 2014-07-16 21:05:12 +0000 |
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committer | John Stultz <john.stultz@linaro.org> | 2014-07-23 15:01:51 -0700 |
commit | 09ec54429c6d10f87d1f084de53ae2c1c3a81108 (patch) | |
tree | 842749293edd755e8bb12e1433c2f9df7dd842cf /arch/x86/kernel | |
parent | 3a97837784acbf9fed699fc04d1799b0eb742fdf (diff) | |
download | op-kernel-dev-09ec54429c6d10f87d1f084de53ae2c1c3a81108.zip op-kernel-dev-09ec54429c6d10f87d1f084de53ae2c1c3a81108.tar.gz |
clocksource: Move cycle_last validation to core code
The only user of the cycle_last validation is the x86 TSC. In order to
provide NMI safe accessor functions for clock monotonic and
monotonic_raw we need to do that in the core.
We can't do the TSC specific
if (now < cycle_last)
now = cycle_last;
for the other wrapping around clocksources, but TSC has
CLOCKSOURCE_MASK(64) which actually does not mask out anything so if
now is less than cycle_last the subtraction will give a negative
result. So we can check for that in clocksource_delta() and return 0
for that case.
Implement and enable it for x86
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Diffstat (limited to 'arch/x86/kernel')
-rw-r--r-- | arch/x86/kernel/tsc.c | 21 |
1 files changed, 9 insertions, 12 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 57e5ce1..456c0e6 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -951,7 +951,7 @@ core_initcall(cpufreq_tsc); static struct clocksource clocksource_tsc; /* - * We compare the TSC to the cycle_last value in the clocksource + * We used to compare the TSC to the cycle_last value in the clocksource * structure to avoid a nasty time-warp. This can be observed in a * very small window right after one CPU updated cycle_last under * xtime/vsyscall_gtod lock and the other CPU reads a TSC value which @@ -961,26 +961,23 @@ static struct clocksource clocksource_tsc; * due to the unsigned delta calculation of the time keeping core * code, which is necessary to support wrapping clocksources like pm * timer. + * + * This sanity check is now done in the core timekeeping code. + * checking the result of read_tsc() - cycle_last for being negative. + * That works because CLOCKSOURCE_MASK(64) does not mask out any bit. */ static cycle_t read_tsc(struct clocksource *cs) { - cycle_t ret = (cycle_t)get_cycles(); - - return ret >= clocksource_tsc.cycle_last ? - ret : clocksource_tsc.cycle_last; -} - -static void resume_tsc(struct clocksource *cs) -{ - if (!boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3)) - clocksource_tsc.cycle_last = 0; + return (cycle_t)get_cycles(); } +/* + * .mask MUST be CLOCKSOURCE_MASK(64). See comment above read_tsc() + */ static struct clocksource clocksource_tsc = { .name = "tsc", .rating = 300, .read = read_tsc, - .resume = resume_tsc, .mask = CLOCKSOURCE_MASK(64), .flags = CLOCK_SOURCE_IS_CONTINUOUS | CLOCK_SOURCE_MUST_VERIFY, |