- 24 7月, 2014 14 次提交
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由 Thomas Gleixner 提交于
Tracers want a correlated time between the kernel instrumentation and user space. We really do not want to export sched_clock() to user space, so we need to provide something sensible for this. Using separate data structures with an non blocking sequence count based update mechanism allows us to do that. The data structure required for the readout has a sequence counter and two copies of the timekeeping data. On the update side: smp_wmb(); tkf->seq++; smp_wmb(); update(tkf->base[0], tk); smp_wmb(); tkf->seq++; smp_wmb(); update(tkf->base[1], tk); On the reader side: do { seq = tkf->seq; smp_rmb(); idx = seq & 0x01; now = now(tkf->base[idx]); smp_rmb(); } while (seq != tkf->seq) So if a NMI hits the update of base[0] it will use base[1] which is still consistent, but this timestamp is not guaranteed to be monotonic across an update. The timestamp is calculated by: now = base_mono + clock_delta * slope So if the update lowers the slope, readers who are forced to the not yet updated second array are still using the old steeper slope. tmono ^ | o n | o n | u | o |o |12345678---> reader order o = old slope u = update n = new slope So reader 6 will observe time going backwards versus reader 5. While other CPUs are likely to be able observe that, the only way for a CPU local observation is when an NMI hits in the middle of the update. Timestamps taken from that NMI context might be ahead of the following timestamps. Callers need to be aware of that and deal with it. V2: Got rid of clock monotonic raw and reorganized the data structures. Folded in the barrier fix from Mathieu. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
Provide a ktime_t based interface for raw monotonic time. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
timekeeping_clocktai() is not used in fast pathes, so the extra timespec conversion is not problematic. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
get_monotonic_boottime() is not used in fast pathes, so the extra timespec conversion is not problematic. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
No more users. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
A lot of code converts either timespecs or ktime_t to nanoseconds. Provide helper functions. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
No more users. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
ktime based conversion function to map a monotonic time stamp to a different CLOCK. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
Speed up the readout. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
Provide a helper function which lets us implement ktime_t based interfaces for real, boot and tai clocks. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
To convert callers of the core code to timespec64 we need to provide the proper interfaces. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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由 Thomas Gleixner 提交于
Right now we have time related prototypes in 3 different header files. Move it to a single timekeeping header file and move the core internal stuff into a core private header. Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Signed-off-by: NJohn Stultz <john.stultz@linaro.org>
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