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>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3be2f788e10d9e0e03ec00e96e581d5e776a1246..2f994caab0b7651f32f5533e601b85a6cd3ee748 100644 (file)
--- 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 b0ecad8ecc34b0c968220991913f893f4d399f27..26a7a28ca110d7efb54c214eab5d854bbd176520 100644 (file)
--- 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,
 };
 
 /*