linux/kernel/trace/trace_clock.c
Tony Luck 58d4e21e50 tracing: Fix wraparound problems in "uptime" trace clock
The "uptime" trace clock added in:

    commit 8aacf017b0
    tracing: Add "uptime" trace clock that uses jiffies

has wraparound problems when the system has been up more
than 1 hour 11 minutes and 34 seconds. It converts jiffies
to nanoseconds using:
        (u64)jiffies_to_usecs(jiffy) * 1000ULL
but since jiffies_to_usecs() only returns a 32-bit value, it
truncates at 2^32 microseconds.  An additional problem on 32-bit
systems is that the argument is "unsigned long", so fixing the
return value only helps until 2^32 jiffies (49.7 days on a HZ=1000
system).

Avoid these problems by using jiffies_64 as our basis, and
not converting to nanoseconds (we do convert to clock_t because
user facing API must not be dependent on internal kernel
HZ values).

Link: http://lkml.kernel.org/p/99d63c5bfe9b320a3b428d773825a37095bf6a51.1405708254.git.tony.luck@intel.com

Cc: stable@vger.kernel.org # 3.10+
Fixes: 8aacf017b0 "tracing: Add "uptime" trace clock that uses jiffies"
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
2014-07-21 09:56:12 -04:00

138 lines
3.4 KiB
C

/*
* tracing clocks
*
* Copyright (C) 2009 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
*
* Implements 3 trace clock variants, with differing scalability/precision
* tradeoffs:
*
* - local: CPU-local trace clock
* - medium: scalable global clock with some jitter
* - global: globally monotonic, serialized clock
*
* Tracer plugins will chose a default from these clocks.
*/
#include <linux/spinlock.h>
#include <linux/irqflags.h>
#include <linux/hardirq.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/ktime.h>
#include <linux/trace_clock.h>
/*
* trace_clock_local(): the simplest and least coherent tracing clock.
*
* Useful for tracing that does not cross to other CPUs nor
* does it go through idle events.
*/
u64 notrace trace_clock_local(void)
{
u64 clock;
/*
* sched_clock() is an architecture implemented, fast, scalable,
* lockless clock. It is not guaranteed to be coherent across
* CPUs, nor across CPU idle events.
*/
preempt_disable_notrace();
clock = sched_clock();
preempt_enable_notrace();
return clock;
}
EXPORT_SYMBOL_GPL(trace_clock_local);
/*
* trace_clock(): 'between' trace clock. Not completely serialized,
* but not completely incorrect when crossing CPUs either.
*
* This is based on cpu_clock(), which will allow at most ~1 jiffy of
* jitter between CPUs. So it's a pretty scalable clock, but there
* can be offsets in the trace data.
*/
u64 notrace trace_clock(void)
{
return local_clock();
}
/*
* trace_jiffy_clock(): Simply use jiffies as a clock counter.
* Note that this use of jiffies_64 is not completely safe on
* 32-bit systems. But the window is tiny, and the effect if
* we are affected is that we will have an obviously bogus
* timestamp on a trace event - i.e. not life threatening.
*/
u64 notrace trace_clock_jiffies(void)
{
return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
}
/*
* trace_clock_global(): special globally coherent trace clock
*
* It has higher overhead than the other trace clocks but is still
* an order of magnitude faster than GTOD derived hardware clocks.
*
* Used by plugins that need globally coherent timestamps.
*/
/* keep prev_time and lock in the same cacheline. */
static struct {
u64 prev_time;
arch_spinlock_t lock;
} trace_clock_struct ____cacheline_aligned_in_smp =
{
.lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED,
};
u64 notrace trace_clock_global(void)
{
unsigned long flags;
int this_cpu;
u64 now;
local_irq_save(flags);
this_cpu = raw_smp_processor_id();
now = sched_clock_cpu(this_cpu);
/*
* If in an NMI context then dont risk lockups and return the
* cpu_clock() time:
*/
if (unlikely(in_nmi()))
goto out;
arch_spin_lock(&trace_clock_struct.lock);
/*
* TODO: if this happens often then maybe we should reset
* my_scd->clock to prev_time+1, to make sure
* we start ticking with the local clock from now on?
*/
if ((s64)(now - trace_clock_struct.prev_time) < 0)
now = trace_clock_struct.prev_time + 1;
trace_clock_struct.prev_time = now;
arch_spin_unlock(&trace_clock_struct.lock);
out:
local_irq_restore(flags);
return now;
}
static atomic64_t trace_counter;
/*
* trace_clock_counter(): simply an atomic counter.
* Use the trace_counter "counter" for cases where you do not care
* about timings, but are interested in strict ordering.
*/
u64 notrace trace_clock_counter(void)
{
return atomic64_add_return(1, &trace_counter);
}