From 14131f2f98ac350ee9e73faed916d2238a8b6a0d Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Thu, 26 Feb 2009 18:47:11 +0100 Subject: tracing: implement trace_clock_*() APIs Impact: implement new tracing timestamp APIs Add three 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 Make the ring-buffer use the local trace clock internally. Acked-by: Peter Zijlstra Acked-by: Steven Rostedt Signed-off-by: Ingo Molnar --- kernel/trace/trace_clock.c | 101 +++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 101 insertions(+) create mode 100644 kernel/trace/trace_clock.c (limited to 'kernel/trace/trace_clock.c') diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c new file mode 100644 index 00000000000..2d4953f9356 --- /dev/null +++ b/kernel/trace/trace_clock.c @@ -0,0 +1,101 @@ +/* + * tracing clocks + * + * Copyright (C) 2009 Red Hat, Inc., Ingo Molnar + * + * 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 +#include +#include +#include +#include +#include + +/* + * 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) +{ + /* + * sched_clock() is an architecture implemented, fast, scalable, + * lockless clock. It is not guaranteed to be coherent across + * CPUs, nor across CPU idle events. + */ + return sched_clock(); +} + +/* + * trace_clock(): 'inbetween' 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 cpu_clock(raw_smp_processor_id()); +} + + +/* + * 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. + */ + +static u64 prev_trace_clock_time; + +static raw_spinlock_t trace_clock_lock ____cacheline_aligned_in_smp = + (raw_spinlock_t)__RAW_SPIN_LOCK_UNLOCKED; + +u64 notrace trace_clock_global(void) +{ + unsigned long flags; + int this_cpu; + u64 now; + + raw_local_irq_save(flags); + + this_cpu = raw_smp_processor_id(); + now = cpu_clock(this_cpu); + /* + * If in an NMI context then dont risk lockups and return the + * cpu_clock() time: + */ + if (unlikely(in_nmi())) + goto out; + + __raw_spin_lock(&trace_clock_lock); + + /* + * TODO: if this happens often then maybe we should reset + * my_scd->clock to prev_trace_clock_time+1, to make sure + * we start ticking with the local clock from now on? + */ + if ((s64)(now - prev_trace_clock_time) < 0) + now = prev_trace_clock_time + 1; + + prev_trace_clock_time = now; + + __raw_spin_unlock(&trace_clock_lock); + + out: + raw_local_irq_restore(flags); + + return now; +} -- cgit v1.2.3 From 6cc3c6e12bb039047974ad2e7e2d46d15a1b762f Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 10 Mar 2009 19:03:43 +0100 Subject: trace_clock: fix preemption bug Using the function_graph tracer in recent kernels generates a spew of preemption BUGs. Fix this by not requiring trace_clock_local() users to disable preemption themselves. Signed-off-by: Peter Zijlstra Cc: Steven Rostedt Cc: Frederic Weisbecker Signed-off-by: Ingo Molnar --- kernel/trace/trace_clock.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) (limited to 'kernel/trace/trace_clock.c') diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c index 2d4953f9356..05b176abfd3 100644 --- a/kernel/trace/trace_clock.c +++ b/kernel/trace/trace_clock.c @@ -27,12 +27,19 @@ */ u64 notrace trace_clock_local(void) { + unsigned long flags; + 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. */ - return sched_clock(); + raw_local_irq_save(flags); + clock = sched_clock(); + raw_local_irq_restore(flags); + + return clock; } /* -- cgit v1.2.3 From b8b94265337f83b7db9c5f429b1769d463d7da8c Mon Sep 17 00:00:00 2001 From: Dmitri Vorobiev Date: Sun, 22 Mar 2009 19:11:11 +0200 Subject: tracing: fix four sparse warnings Impact: cleanup. This patch fixes the following sparse warnings: kernel/trace/trace.c:385:9: warning: symbol 'trace_seq_to_buffer' was not declared. Should it be static? kernel/trace/trace_clock.c:29:13: warning: symbol 'trace_clock_local' was not declared. Should it be static? kernel/trace/trace_clock.c:54:13: warning: symbol 'trace_clock' was not declared. Should it be static? kernel/trace/trace_clock.c:74:13: warning: symbol 'trace_clock_global' was not declared. Should it be static? Signed-off-by: Dmitri Vorobiev LKML-Reference: <1237741871-5827-4-git-send-email-dmitri.vorobiev@movial.com> Signed-off-by: Ingo Molnar --- kernel/trace/trace_clock.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/trace/trace_clock.c') diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c index 05b176abfd3..b588fd81f7f 100644 --- a/kernel/trace/trace_clock.c +++ b/kernel/trace/trace_clock.c @@ -18,6 +18,7 @@ #include #include #include +#include /* * trace_clock_local(): the simplest and least coherent tracing clock. -- cgit v1.2.3