tracing: add global-clock option to provide cross CPU clock to traces

Impact: feature to allow better serialized clock

This patch adds an option called "global-clock" that will allow
the tracer to switch to a slower but more accurate (across CPUs)
clock.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>

2 files changed, 31 insertions, 4 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3be2f788e10d..2f994caab0b7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -315,6 +315,7 @@ static const char *trace_options[] = {
         "printk-msg-only",
         "context-info",
         "latency-format",
+        "global-clock",
         NULL
 };
 
@@ -2251,6 +2252,34 @@ static int set_tracer_option(struct tracer *trace, char *cmp, int neg)
         return 0;
 }
 
+static void set_tracer_flags(unsigned int mask, int enabled)
+{
+        /* do nothing if flag is already set */
+        if (!!(trace_flags & mask) == !!enabled)
+                return;
+
+        if (enabled)
+                trace_flags |= mask;
+        else
+                trace_flags &= ~mask;
+
+        if (mask == TRACE_ITER_GLOBAL_CLK) {
+                u64 (*func)(void);
+
+                if (enabled)
+                        func = trace_clock_global;
+                else
+                        func = trace_clock_local;
+
+                mutex_lock(&trace_types_lock);
+                ring_buffer_set_clock(global_trace.buffer, func);
+
+                if (max_tr.buffer)
+                        ring_buffer_set_clock(max_tr.buffer, func);
+                mutex_unlock(&trace_types_lock);
+        }
+}
+
 static ssize_t
 tracing_trace_options_write(struct file *filp, const char __user *ubuf,
                         size_t cnt, loff_t *ppos)
@@ -2278,10 +2307,7 @@ tracing_trace_options_write(struct file *filp, const char __user *ubuf,
                 int len = strlen(trace_options[i]);
 
                 if (strncmp(cmp, trace_options[i], len) == 0) {
-                        if (neg)
-                                trace_flags &= ~(1 << i);
-                        else
-                                trace_flags |= (1 << i);
+                        set_tracer_flags(1 << i, !neg);
                         break;
                 }
         }
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index b0ecad8ecc34..26a7a28ca110 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -667,6 +667,7 @@ enum trace_iterator_flags {
         TRACE_ITER_PRINTK_MSGONLY       = 0x10000,
         TRACE_ITER_CONTEXT_INFO         = 0x20000, /* Print pid/cpu/time */
         TRACE_ITER_LATENCY_FMT          = 0x40000,
+        TRACE_ITER_GLOBAL_CLK           = 0x80000,
 };
 
 /*