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Date: Tue, 3 Mar 2020 08:08:46 +0100
From: Thomas Richter <tmricht@...ux.ibm.com>
To: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
acme@...nel.org
Cc: gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
heiko.carstens@...ibm.com, Thomas Richter <tmricht@...ux.ibm.com>
Subject: [PATCH] perf documentation: Add desription forHEADER_TRACING_DATA
Add description and layout in the perf.data file for
the header part describing trace data used in commands
perf record -e XXX
where XXX is a probe or tracepoint.
Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
---
.../Documentation/perf.data-file-format.txt | 106 +++++++++++++++++-
1 file changed, 105 insertions(+), 1 deletion(-)
diff --git a/tools/perf/Documentation/perf.data-file-format.txt b/tools/perf/Documentation/perf.data-file-format.txt
index b0152e1095c5..e3f78269e417 100644
--- a/tools/perf/Documentation/perf.data-file-format.txt
+++ b/tools/perf/Documentation/perf.data-file-format.txt
@@ -67,9 +67,113 @@ flags. These define the valid bits:
HEADER_RESERVED = 0, /* always cleared */
HEADER_FIRST_FEATURE = 1,
+
HEADER_TRACING_DATA = 1,
-Describe me.
+The header consists of several entries of variable length such as file
+contents of several trace files like 'header_page', 'header_event'.
+Also complete probe/<event-name>/format files are included.
+The numbers in parenthesis are structure members refered to later in
+the description and example.
+
+struct tracing_data {
+ char birthday[3] = { 23, 8, 68 }; Eyecatcher
+ char tracing[12] = "tracing0.6"; Type and version
+ uint8_t bigendian; Big or little endian platform
+ uint8_t sizelong; Size of long in bytes
+ uint32_t pagesize: Pagesize in bytes
+ char hdr_page[12] = "header_page" Name of file (1)
+ uint64_t hdr_page_size; File size in bytes (1a)
+ char hdr_page_contents[hdr_page_size]; Contents of file (1b)
+ char hdr_event[13] = "header_event" Name of file (2)
+ uint64_t hdr_event_size; File size in bytes
+ char hdr_page_contents[hdr_event_size]; Contents of file
+ uint32_t ftrace_count; Number of ftrace entries (3)
+ struct { Size and content of file
+ uint64_t file_size;
+ char file_content[file_size]
+ } ftrace[ftrace_count] ftrace_count array elements
+ uint32_t event_types; Number of event types (4)
+ struct {
+ char name[]; Name, null terminatedg (5)
+ uint32_t count; Number of probes (6)
+ struct {
+ uint64_t file_size; (7)
+ char file_content[file_size]; (8)
+ }[count]; Count always > 0 or omitted
+ }[event_types];
+ uint32_t proc_kallsyms_size; Always zero
+ uint64_t printk_file_size; File size in bytes (9)
+ char printk_format[printk_file_size]; Contents of file
+ uint64_t saved_cmdlines_size; File size in bytes (10)
+ char saved_cmdlines[saved_cmdlines_size]; Contents of file
+};
+
+The structure description is straight forward. It contains file name, size
+and contents from
+- /sys/kernel/debug/tracing/events/header_page (1, 1a, 1b)
+and
+- /sys/kernel/debug/tracing/events/header_event (2).
+
+This is followed by a variable length part of format files found in directory
+/sys/kernel/debug/tracing//events/ftrace/*/format for events selected
+by the perf record -e XXX commands. Note member 'ftrace_count' can be zero.
+
+Next are the number of probe types specified by the perf record -e XXXX
+command (4). Each type has stored its name (5), which is a null terminated
+string, and the number of probes (6) belonging to this type. For each
+active probe follows the file size (7) and file contents (8) of that probe.
+
+Finally the file size and contents of two more files is saved:
+- Size of /proc/kallsyms (always hard coded to zero and no file contents)
+- /sys/kernel/debug/tracing/printk_formats (9)
+- /sys/kernel/debug/tracing/saved_cmdlines (10)
+
+Example for the dynamic probes and trace points:
+Consider these probes have been set up:
+ # ./perf probe -l
+ probe:vfs_getname (on getname_flags:72@...namei.c with pathname)
+ probe:xxx (on do_file_open_root:11@...namei.c)
+ #
+and this command used for recording:
+ # ./perf record -e probe:vfs_getname -e probe:xxx \
+ -e tcp:tcp_retransmit_skb -- touch /tmp/xxx
+
+This command line leads to two events in directory
+ /sys/kernel/debug/tracing/events/probe/vfs_getname
+ /sys/kernel/debug/tracing/events/probe/xxx
+and a tracepoint in directory
+ /sys/kernel/debug/tracing/events/tcp/tcp_retransmit_skb.
+
+This results in this event_count (5) layout in the perf.data:
+using command:
+ # od -Ax -t x4z -v perf.data
+
+0011a0 00000000 00000270 726f6265 00000000 >.......probe....<
+ ^^ (4)^^^'' ''(5)''' ''--(6)-
+ 4: # of types --> 2
+ 5: first one named 'probe'
+ 6: 2 probes defined
+0011b0 02000000 00000001 766e616d 653a2078 >........vname: x<
+ --###### (7)##### ##
+ 7: first one 'named' xxx with format file size 0x176
+0011c0 78780a49 443a2031 3138360a 666f726d >xx.ID: 1186.form<
+...
+001320 45432d3e 5f5f7072 6f62655f 69700a00 >EC->__probe_ip..<
+ ''
+001330 00000000 0001e36e 616d653a 20766673 >.......name: vfs<
+ ''(7)''' ''''''
+ 7: second one named 'vfs_getname' with format file size 0x1e3
+001340 5f676574 6e616d65 0a49443a 20313138 >_getname.ID: 118<
+...
+001510 70617468 6e616d65 290a7463 70000000 >pathname).tcp...<
+ ''(5 )'--(6)-
+001520 00010000 00000000 05696e61 6d653a20 >.........iname: <
+ ----#### (7)##### ####
+ 5: second event type named 'tcp'
+ 6: 1 probe defined
+ 7: size of format file 0x568
+001530 7463705f 72657472 616e736d 69745f73 >tcp_retransmit_s<
HEADER_BUILD_ID = 2,
--
2.23.0
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