LCOV - code coverage report
Current view: top level - kernel/trace - trace_clock.c (source / functions) Hit Total Coverage
Test: gcov_data_raspi2_real_modules_combined.info Lines: 5 20 25.0 %
Date: 2020-09-30 20:25:40 Functions: 1 5 20.0 %
Branches: 0 4 0.0 %

           Branch data     Line data    Source code
       1                 :            : // SPDX-License-Identifier: GPL-2.0
       2                 :            : /*
       3                 :            :  * tracing clocks
       4                 :            :  *
       5                 :            :  *  Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
       6                 :            :  *
       7                 :            :  * Implements 3 trace clock variants, with differing scalability/precision
       8                 :            :  * tradeoffs:
       9                 :            :  *
      10                 :            :  *  -   local: CPU-local trace clock
      11                 :            :  *  -  medium: scalable global clock with some jitter
      12                 :            :  *  -  global: globally monotonic, serialized clock
      13                 :            :  *
      14                 :            :  * Tracer plugins will chose a default from these clocks.
      15                 :            :  */
      16                 :            : #include <linux/spinlock.h>
      17                 :            : #include <linux/irqflags.h>
      18                 :            : #include <linux/hardirq.h>
      19                 :            : #include <linux/module.h>
      20                 :            : #include <linux/percpu.h>
      21                 :            : #include <linux/sched.h>
      22                 :            : #include <linux/sched/clock.h>
      23                 :            : #include <linux/ktime.h>
      24                 :            : #include <linux/trace_clock.h>
      25                 :            : 
      26                 :            : /*
      27                 :            :  * trace_clock_local(): the simplest and least coherent tracing clock.
      28                 :            :  *
      29                 :            :  * Useful for tracing that does not cross to other CPUs nor
      30                 :            :  * does it go through idle events.
      31                 :            :  */
      32                 :      14904 : u64 notrace trace_clock_local(void)
      33                 :            : {
      34                 :            :         u64 clock;
      35                 :            : 
      36                 :            :         /*
      37                 :            :          * sched_clock() is an architecture implemented, fast, scalable,
      38                 :            :          * lockless clock. It is not guaranteed to be coherent across
      39                 :            :          * CPUs, nor across CPU idle events.
      40                 :            :          */
      41                 :      14904 :         preempt_disable_notrace();
      42                 :      14904 :         clock = sched_clock();
      43                 :      14904 :         preempt_enable_notrace();
      44                 :            : 
      45                 :      14904 :         return clock;
      46                 :            : }
      47                 :            : EXPORT_SYMBOL_GPL(trace_clock_local);
      48                 :            : 
      49                 :            : /*
      50                 :            :  * trace_clock(): 'between' trace clock. Not completely serialized,
      51                 :            :  * but not completely incorrect when crossing CPUs either.
      52                 :            :  *
      53                 :            :  * This is based on cpu_clock(), which will allow at most ~1 jiffy of
      54                 :            :  * jitter between CPUs. So it's a pretty scalable clock, but there
      55                 :            :  * can be offsets in the trace data.
      56                 :            :  */
      57                 :          0 : u64 notrace trace_clock(void)
      58                 :            : {
      59                 :          0 :         return local_clock();
      60                 :            : }
      61                 :            : EXPORT_SYMBOL_GPL(trace_clock);
      62                 :            : 
      63                 :            : /*
      64                 :            :  * trace_jiffy_clock(): Simply use jiffies as a clock counter.
      65                 :            :  * Note that this use of jiffies_64 is not completely safe on
      66                 :            :  * 32-bit systems. But the window is tiny, and the effect if
      67                 :            :  * we are affected is that we will have an obviously bogus
      68                 :            :  * timestamp on a trace event - i.e. not life threatening.
      69                 :            :  */
      70                 :          0 : u64 notrace trace_clock_jiffies(void)
      71                 :            : {
      72                 :          0 :         return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
      73                 :            : }
      74                 :            : EXPORT_SYMBOL_GPL(trace_clock_jiffies);
      75                 :            : 
      76                 :            : /*
      77                 :            :  * trace_clock_global(): special globally coherent trace clock
      78                 :            :  *
      79                 :            :  * It has higher overhead than the other trace clocks but is still
      80                 :            :  * an order of magnitude faster than GTOD derived hardware clocks.
      81                 :            :  *
      82                 :            :  * Used by plugins that need globally coherent timestamps.
      83                 :            :  */
      84                 :            : 
      85                 :            : /* keep prev_time and lock in the same cacheline. */
      86                 :            : static struct {
      87                 :            :         u64 prev_time;
      88                 :            :         arch_spinlock_t lock;
      89                 :            : } trace_clock_struct ____cacheline_aligned_in_smp =
      90                 :            :         {
      91                 :            :                 .lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
      92                 :            :         };
      93                 :            : 
      94                 :          0 : u64 notrace trace_clock_global(void)
      95                 :            : {
      96                 :            :         unsigned long flags;
      97                 :            :         int this_cpu;
      98                 :            :         u64 now;
      99                 :            : 
     100                 :            :         raw_local_irq_save(flags);
     101                 :            : 
     102                 :          0 :         this_cpu = raw_smp_processor_id();
     103                 :          0 :         now = sched_clock_cpu(this_cpu);
     104                 :            :         /*
     105                 :            :          * If in an NMI context then dont risk lockups and return the
     106                 :            :          * cpu_clock() time:
     107                 :            :          */
     108         [ #  # ]:          0 :         if (unlikely(in_nmi()))
     109                 :            :                 goto out;
     110                 :            : 
     111                 :          0 :         arch_spin_lock(&trace_clock_struct.lock);
     112                 :            : 
     113                 :            :         /*
     114                 :            :          * TODO: if this happens often then maybe we should reset
     115                 :            :          * my_scd->clock to prev_time+1, to make sure
     116                 :            :          * we start ticking with the local clock from now on?
     117                 :            :          */
     118         [ #  # ]:          0 :         if ((s64)(now - trace_clock_struct.prev_time) < 0)
     119                 :          0 :                 now = trace_clock_struct.prev_time + 1;
     120                 :            : 
     121                 :          0 :         trace_clock_struct.prev_time = now;
     122                 :            : 
     123                 :            :         arch_spin_unlock(&trace_clock_struct.lock);
     124                 :            : 
     125                 :            :  out:
     126                 :            :         raw_local_irq_restore(flags);
     127                 :            : 
     128                 :          0 :         return now;
     129                 :            : }
     130                 :            : EXPORT_SYMBOL_GPL(trace_clock_global);
     131                 :            : 
     132                 :            : static atomic64_t trace_counter;
     133                 :            : 
     134                 :            : /*
     135                 :            :  * trace_clock_counter(): simply an atomic counter.
     136                 :            :  * Use the trace_counter "counter" for cases where you do not care
     137                 :            :  * about timings, but are interested in strict ordering.
     138                 :            :  */
     139                 :          0 : u64 notrace trace_clock_counter(void)
     140                 :            : {
     141                 :          0 :         return atomic64_add_return(1, &trace_counter);
     142                 :            : }

Generated by: LCOV version 1.14