Patchwork [1/2] trace: Add ftrace tracing backend

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Submitter Eiichi Tsukata
Date April 3, 2013, 6:30 a.m.
Message ID <1364970659-5715-2-git-send-email-eiichi.tsukata.xh@hitachi.com>
Download mbox | patch
Permalink /patch/233296/
State New
Headers show

Comments

Eiichi Tsukata - April 3, 2013, 6:30 a.m.
This patch adds a ftrace tracing backend which sends trace event to
ftrace marker file. You can effectively compare qemu trace data and
kernel(especially, kvm.ko when using KVM) trace data.
The ftrace backend is restricted to Linux only.

To try out the ftrace backend:

 $ ./configure --trace-backend=ftrace
 $ make

if you use KVM, enable kvm events in ftrace:

 # sudo echo 1 > /sys/kernel/debug/tracing/events/kvm/enable

After running qemu by root user, you can get the trace:

 # cat /sys/kernel/debug/tracing/trace

Signed-off-by: Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
---
 configure                           |   8 +++
 scripts/tracetool/backend/ftrace.py |  53 +++++++++++++++++++
 trace/Makefile.objs                 |   1 +
 trace/ftrace.c                      | 102 ++++++++++++++++++++++++++++++++++++
 trace/ftrace.h                      |  10 ++++
 5 files changed, 174 insertions(+)
 create mode 100644 scripts/tracetool/backend/ftrace.py
 create mode 100644 trace/ftrace.c
 create mode 100644 trace/ftrace.h
Stefan Hajnoczi - April 8, 2013, 2:10 p.m.
On Wed, Apr 03, 2013 at 03:30:58PM +0900, Eiichi Tsukata wrote:
> diff --git a/scripts/tracetool/backend/ftrace.py b/scripts/tracetool/backend/ftrace.py
> new file mode 100644
> index 0000000..e02f0ca
> --- /dev/null
> +++ b/scripts/tracetool/backend/ftrace.py
> @@ -0,0 +1,53 @@
> +#!/usr/bin/env python
> +# -*- coding: utf-8 -*-
> +
> +"""
> +Ftrace built-in backend.
> +"""
> +
> +__author__     = "Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>"
> +__copyright__  = "Copyright (C) 2013 Hitachi, Ltd."
> +__license__    = "GPL version 2 or (at your option) any later version"
> +
> +__maintainer__ = "Stefan Hajnoczi"
> +__email__      = "stefanha@linux.vnet.ibm.com"

My email is now stefanha@redhat.com.  I can fix this up when merging the
patch.

> +        out('static inline void trace_%(name)s(%(args)s)',
> +            '{',
> +            '    char ftrace_buf[MAX_TRACE_STRLEN];',
> +            '    int unused __attribute__ ((unused));'
> +            '    bool _state = trace_event_get_state(%(event_id)s);',
> +            '    if (_state) {',
> +            '        snprintf(ftrace_buf, MAX_TRACE_STRLEN,',
> +            '                 "%(name)s " %(fmt)s "\\n" %(argnames)s);',
> +            '        unused = write(trace_marker_fd, ftrace_buf,',
> +            '                       MAX_TRACE_STRLEN);',

Looking at kernel/trace/trace.c:tracing_mark_write() the kernel will
memcpy() the full number of bytes we give.

You could use the snprintf(3) return value (number of characters
written, excluding NUL byte).

I think that would waste less trace buffer space.

Stefan
Eiichi Tsukata - April 9, 2013, 10:47 a.m.
Hello Stefan,

Thank you for reviewing my patch.

(2013/04/08 23:10), Stefan Hajnoczi wrote:
> On Wed, Apr 03, 2013 at 03:30:58PM +0900, Eiichi Tsukata wrote:
>> diff --git a/scripts/tracetool/backend/ftrace.py b/scripts/tracetool/backend/ftrace.py
>> new file mode 100644
>> index 0000000..e02f0ca
>> --- /dev/null
>> +++ b/scripts/tracetool/backend/ftrace.py
>> @@ -0,0 +1,53 @@
>> +#!/usr/bin/env python
>> +# -*- coding: utf-8 -*-
>> +
>> +"""
>> +Ftrace built-in backend.
>> +"""
>> +
>> +__author__     = "Eiichi Tsukata<eiichi.tsukata.xh@hitachi.com>"
>> +__copyright__  = "Copyright (C) 2013 Hitachi, Ltd."
>> +__license__    = "GPL version 2 or (at your option) any later version"
>> +
>> +__maintainer__ = "Stefan Hajnoczi"
>> +__email__      = "stefanha@linux.vnet.ibm.com"
>
> My email is now stefanha@redhat.com.  I can fix this up when merging the
> patch.

I see, I'll fix it up.

>
>> +        out('static inline void trace_%(name)s(%(args)s)',
>> +            '{',
>> +            '    char ftrace_buf[MAX_TRACE_STRLEN];',
>> +            '    int unused __attribute__ ((unused));'
>> +            '    bool _state = trace_event_get_state(%(event_id)s);',
>> +            '    if (_state) {',
>> +            '        snprintf(ftrace_buf, MAX_TRACE_STRLEN,',
>> +            '                 "%(name)s " %(fmt)s "\\n" %(argnames)s);',
>> +            '        unused = write(trace_marker_fd, ftrace_buf,',
>> +            '                       MAX_TRACE_STRLEN);',
>
> Looking at kernel/trace/trace.c:tracing_mark_write() the kernel will
> memcpy() the full number of bytes we give.
>
> You could use the snprintf(3) return value (number of characters
> written, excluding NUL byte).
>
> I think that would waste less trace buffer space.
>

Sounds good.
I'll use snprintf(3) return value in V2 patch and send it soon.

Eiichi

> Stefan
> .
>

Patch

diff --git a/configure b/configure
index f2af714..6cbed00 100755
--- a/configure
+++ b/configure
@@ -3848,6 +3848,14 @@  if test "$trace_backend" = "dtrace"; then
     echo "CONFIG_TRACE_SYSTEMTAP=y" >> $config_host_mak
   fi
 fi
+if test "$trace_backend" = "ftrace"; then
+  if test "$linux" = "yes" ; then
+    echo "CONFIG_TRACE_FTRACE=y" >> $config_host_mak
+    trace_default=no
+  else
+    feature_not_found "ftrace(trace backend)"
+  fi
+fi
 echo "CONFIG_TRACE_FILE=$trace_file" >> $config_host_mak
 if test "$trace_default" = "yes"; then
   echo "CONFIG_TRACE_DEFAULT=y" >> $config_host_mak
diff --git a/scripts/tracetool/backend/ftrace.py b/scripts/tracetool/backend/ftrace.py
new file mode 100644
index 0000000..e02f0ca
--- /dev/null
+++ b/scripts/tracetool/backend/ftrace.py
@@ -0,0 +1,53 @@ 
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+
+"""
+Ftrace built-in backend.
+"""
+
+__author__     = "Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>"
+__copyright__  = "Copyright (C) 2013 Hitachi, Ltd."
+__license__    = "GPL version 2 or (at your option) any later version"
+
+__maintainer__ = "Stefan Hajnoczi"
+__email__      = "stefanha@linux.vnet.ibm.com"
+
+
+from tracetool import out
+
+
+PUBLIC = True
+
+
+def c(events):
+    pass
+
+def h(events):
+    out('#include "trace/ftrace.h"',
+        '#include "trace/control.h"',
+        '',
+        )
+
+    for e in events:
+        argnames = ", ".join(e.args.names())
+        if len(e.args) > 0:
+            argnames = ", " + argnames
+
+        out('static inline void trace_%(name)s(%(args)s)',
+            '{',
+            '    char ftrace_buf[MAX_TRACE_STRLEN];',
+            '    int unused __attribute__ ((unused));'
+            '    bool _state = trace_event_get_state(%(event_id)s);',
+            '    if (_state) {',
+            '        snprintf(ftrace_buf, MAX_TRACE_STRLEN,',
+            '                 "%(name)s " %(fmt)s "\\n" %(argnames)s);',
+            '        unused = write(trace_marker_fd, ftrace_buf,',
+            '                       MAX_TRACE_STRLEN);',
+            '    }',
+            '}',
+            name = e.name,
+            args = e.args,
+            event_id = "TRACE_" + e.name.upper(),
+            fmt = e.fmt.rstrip("\n"),
+            argnames = argnames,
+            )
diff --git a/trace/Makefile.objs b/trace/Makefile.objs
index a043072..3b88e49 100644
--- a/trace/Makefile.objs
+++ b/trace/Makefile.objs
@@ -76,5 +76,6 @@  endif
 util-obj-$(CONFIG_TRACE_DEFAULT) += default.o
 util-obj-$(CONFIG_TRACE_SIMPLE) += simple.o
 util-obj-$(CONFIG_TRACE_STDERR) += stderr.o
+util-obj-$(CONFIG_TRACE_FTRACE) += ftrace.o
 util-obj-y += control.o
 util-obj-y += generated-tracers.o
diff --git a/trace/ftrace.c b/trace/ftrace.c
new file mode 100644
index 0000000..46b7fdb
--- /dev/null
+++ b/trace/ftrace.c
@@ -0,0 +1,102 @@ 
+/*
+ * Ftrace trace backend
+ *
+ * Copyright (C) 2013 Hitachi, Ltd.
+ * Created by Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <fcntl.h>
+#include <limits.h>
+#include "trace.h"
+#include "trace/control.h"
+
+int trace_marker_fd;
+
+static int find_debugfs(char *debugfs)
+{
+    char type[100];
+    FILE *fp;
+
+    fp = fopen("/proc/mounts", "r");
+    if (fp == NULL) {
+        return 0;
+    }
+
+    while (fscanf(fp, "%*s %" STR(PATH_MAX) "s %99s %*s %*d %*d\n",
+                  debugfs, type) == 2) {
+        if (strcmp(type, "debugfs") == 0) {
+            break;
+        }
+    }
+    fclose(fp);
+
+    if (strcmp(type, "debugfs") != 0) {
+        return 0;
+    }
+    return 1;
+}
+
+void trace_print_events(FILE *stream, fprintf_function stream_printf)
+{
+    TraceEventID i;
+
+    for (i = 0; i < trace_event_count(); i++) {
+        TraceEvent *ev = trace_event_id(i);
+        stream_printf(stream, "%s [Event ID %u] : state %u\n",
+                      trace_event_get_name(ev), i, trace_event_get_state_dynamic(ev));
+    }
+}
+
+void trace_event_set_state_dynamic_backend(TraceEvent *ev, bool state)
+{
+    ev->dstate = state;
+}
+
+bool trace_backend_init(const char *events, const char *file)
+{
+    char debugfs[PATH_MAX];
+    char path[PATH_MAX];
+    int debugfs_found;
+    int trace_fd = -1;
+
+    if (file) {
+        fprintf(stderr, "error: -trace file=...: "
+                "option not supported by the selected tracing backend\n");
+        return false;
+    }
+
+    debugfs_found = find_debugfs(debugfs);
+    if (debugfs_found) {
+        snprintf(path, PATH_MAX, "%s/tracing/tracing_on", debugfs);
+        trace_fd = open(path, O_WRONLY);
+        if (trace_fd < 0) {
+            perror("Could not open ftrace 'tracing_on' file");
+            return false;
+        } else {
+            if (write(trace_fd, "1", 1) < 0) {
+                perror("Could not write to 'tracing_on' file");
+                close(trace_fd);
+                return false;
+            }
+            close(trace_fd);
+        }
+        snprintf(path, PATH_MAX, "%s/tracing/trace_marker", debugfs);
+        trace_marker_fd = open(path, O_WRONLY);
+        if (trace_marker_fd < 0) {
+            perror("Could not open ftrace 'trace_marker' file");
+            return false;
+        }
+    } else {
+        fprintf(stderr, "debugfs is not mounted\n");
+        return false;
+    }
+
+    trace_backend_init_events(events);
+    return true;
+}
diff --git a/trace/ftrace.h b/trace/ftrace.h
new file mode 100644
index 0000000..94cb8d5
--- /dev/null
+++ b/trace/ftrace.h
@@ -0,0 +1,10 @@ 
+#ifndef TRACE_FTRACE_H
+#define TRACE_FTRACE_H
+
+#define MAX_TRACE_STRLEN 512
+#define _STR(x) #x
+#define STR(x) _STR(x)
+
+extern int trace_marker_fd;
+
+#endif /* ! TRACE_FTRACE_H */