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Subject[PATCH 2/5] tracing: add global-clock option to provide cross CPU clock to traces
From: Steven Rostedt <srostedt@redhat.com>

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>
---
kernel/trace/trace.c | 34 ++++++++++++++++++++++++++++++----
kernel/trace/trace.h | 1 +
2 files changed, 31 insertions(+), 4 deletions(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 3be2f78..2f994ca 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 b0ecad8..26a7a28 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,
};

/*
--
1.6.2
--


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