[PATCH V7 0/3] Integration of function trace with System Trace IP blocks

From: Chunyan Zhang
Date: Tue Oct 18 2016 - 04:09:28 EST

IP blocks allowing a variety of trace sources to log debugging
information to a pre-defined area have been introduced on a couple of
architecture [1][2]. These system trace blocks (also known as STM)
typically follow the MIPI STPv2 protocol [3] and provide a system wide
logging facility to any device, running a kernel or not, with access
to the block's log entry port(s). Since each trace message has a
timestamp, it is possible to correlate events happening in the entire
system rather than being confined to the logging facility of a single

This patchset is trying to use STM IP blocks to store function tracing
information produced by Ftrace and I'm taking the Function trace
(trace type is TRACE_FN) as the example in this patchset, but other
types of traces also can be supported.

Logging information generated by the Ftrace subsystem to STM and gathered
in the sink device can be used in conjunction with trace data from other
board components, also collected in the same trace sink.

This example is using ARM coresight STM but the same would apply to any
other architecture wishing to do the same.

Comments would be greatly appreciated.


[1]. https://lwn.net/Articles/674746/
[2]. http://lxr.free-electrons.com/source/drivers/hwtracing/intel_th/
[3]. http://mipi.org/specifications/debug#STP

Changes from v6:
* Rebased on v4.9-rc1;
* Removed unused the declaration and header file including from trace.h
which was added in patch 1 of this series;
* Revised a bit the comments in trace.h .

Changes from v5:
* Addressed comments from Steven Rostedt:
- Removed .commit() from trace_export;
- Changed to directly call trace_process_export() instead of trace_export::commit();
- Used 'ring_buffer_event_length(event)' instead to get the trace size;
- Removed trace_export pointer from trace_array structure.
* Revised commit message a little to make the description more accurate.

Changes from v4:
* Addressed comments from Steven Rostedt:
- Removed 'inline' annotations from the function which is called via function pointer;
- Removed useless components from structure trace_export;
- Added '__rcu' annotation to the RCU variables;
- Used 'rcu_assign_pointer' to do every RCU assignment;
- Added WARN_ON_ONCE() when the .write() is not assigned;
- In order to reduce the overhead caused by adding this feature, this revision used an
global array instead of a big "if statement" to get the size of trace entry according
to the trace type.
- In order to keep the current logic unchanged, made ftrace_exports() only being called if
there's something have been added, i.e. if trace_export to stm_ftrace has been added in
this patchset.

Changes from v3:
* Addressed comments from Steven Rostedt:
- Added comments for the element 'name' and 'next' of trace_export;
- Changed to use RCU functions instead of mutex in function callback;
- Moved the check for name to register trace_export function;
* Renamed 'trace_function_exports' to 'trace_exports' since its
implementation is not only for function_trace; The similar changes on
'add_trace_export' and 'rm_trace_export'.

Changes from v2:
* Rebased on v4.8-rc1.
* Added trace_export class, and make traces can be exported to not only
ring buffer but also other area such as STM.
* Made stm_ftrace as an trace_export.
* More detailed changes are described in change log of each patch.

Changes from v1:
* Addressed comments from Alexander Shishkin:
- Modified some ambiguous change logs.
- Decoupled stm_ftrace and trace_output interface to STM.
- Changed the file name from stm_ftrace.c to stm/ftrace.c.
- Implemented link/unlink hooks for stm_ftrace.
* Removed useless header file include from stm/ftrace.c
* Added Acked-by from Steven Rostedt on 4/4.

Chunyan Zhang (3):
tracing: add a possibility of exporting function trace to other places
instead of ring buffer only
stm class: ftrace: Add ftrace-export-over-stm driver
stm: Mark the functions of writing buffer with notrace

drivers/hwtracing/coresight/coresight-stm.c | 2 +-
drivers/hwtracing/intel_th/sth.c | 11 ++-
drivers/hwtracing/stm/Kconfig | 11 +++
drivers/hwtracing/stm/Makefile | 2 +
drivers/hwtracing/stm/core.c | 7 +-
drivers/hwtracing/stm/dummy_stm.c | 2 +-
drivers/hwtracing/stm/ftrace.c | 88 +++++++++++++++++++
include/linux/stm.h | 4 +-
include/linux/trace.h | 28 ++++++
kernel/trace/trace.c | 132 +++++++++++++++++++++++++++-
10 files changed, 275 insertions(+), 12 deletions(-)
create mode 100644 drivers/hwtracing/stm/ftrace.c
create mode 100644 include/linux/trace.h