diff options
Diffstat (limited to 'Documentation/trace')
| -rw-r--r-- | Documentation/trace/ftrace-uses.rst | 10 | ||||
| -rw-r--r-- | Documentation/trace/ftrace.rst | 4 | ||||
| -rw-r--r-- | Documentation/trace/intel_th.rst | 28 |
3 files changed, 39 insertions, 3 deletions
diff --git a/Documentation/trace/ftrace-uses.rst b/Documentation/trace/ftrace-uses.rst index 1fbc69894eed..2a05e770618a 100644 --- a/Documentation/trace/ftrace-uses.rst +++ b/Documentation/trace/ftrace-uses.rst @@ -146,7 +146,7 @@ FTRACE_OPS_FL_RECURSION_SAFE itself or any nested functions that those functions call. If this flag is set, it is possible that the callback will also - be called with preemption enabled (when CONFIG_PREEMPT is set), + be called with preemption enabled (when CONFIG_PREEMPTION is set), but this is not guaranteed. FTRACE_OPS_FL_IPMODIFY @@ -170,6 +170,14 @@ FTRACE_OPS_FL_RCU a callback may be executed and RCU synchronization will not protect it. +FTRACE_OPS_FL_PERMANENT + If this is set on any ftrace ops, then the tracing cannot disabled by + writing 0 to the proc sysctl ftrace_enabled. Equally, a callback with + the flag set cannot be registered if ftrace_enabled is 0. + + Livepatch uses it not to lose the function redirection, so the system + stays protected. + Filtering which functions to trace ================================== diff --git a/Documentation/trace/ftrace.rst b/Documentation/trace/ftrace.rst index e3060eedb22d..d2b5657ed33e 100644 --- a/Documentation/trace/ftrace.rst +++ b/Documentation/trace/ftrace.rst @@ -2976,7 +2976,9 @@ Note, the proc sysctl ftrace_enable is a big on/off switch for the function tracer. By default it is enabled (when function tracing is enabled in the kernel). If it is disabled, all function tracing is disabled. This includes not only the function tracers for ftrace, but -also for any other uses (perf, kprobes, stack tracing, profiling, etc). +also for any other uses (perf, kprobes, stack tracing, profiling, etc). It +cannot be disabled if there is a callback with FTRACE_OPS_FL_PERMANENT set +registered. Please disable this with care. diff --git a/Documentation/trace/intel_th.rst b/Documentation/trace/intel_th.rst index baa12eb09ef4..70b7126eaeeb 100644 --- a/Documentation/trace/intel_th.rst +++ b/Documentation/trace/intel_th.rst @@ -44,7 +44,8 @@ Documentation/trace/stm.rst for more information on that. MSU can be configured to collect trace data into a system memory buffer, which can later on be read from its device nodes via read() or -mmap() interface. +mmap() interface and directed to a "software sink" driver that will +consume the data and/or relay it further. On the whole, Intel(R) Trace Hub does not require any special userspace software to function; everything can be configured, started @@ -122,3 +123,28 @@ In order to enable the host mode, set the 'host_mode' parameter of the will show up on the intel_th bus. Also, trace configuration and capture controlling attribute groups of the 'gth' device will not be exposed. The 'sth' device will operate as usual. + +Software Sinks +-------------- + +The Memory Storage Unit (MSU) driver provides an in-kernel API for +drivers to register themselves as software sinks for the trace data. +Such drivers can further export the data via other devices, such as +USB device controllers or network cards. + +The API has two main parts:: + - notifying the software sink that a particular window is full, and + "locking" that window, that is, making it unavailable for the trace + collection; when this happens, the MSU driver will automatically + switch to the next window in the buffer if it is unlocked, or stop + the trace capture if it's not; + - tracking the "locked" state of windows and providing a way for the + software sink driver to notify the MSU driver when a window is + unlocked and can be used again to collect trace data. + +An example sink driver, msu-sink illustrates the implementation of a +software sink. Functionally, it simply unlocks windows as soon as they +are full, keeping the MSU running in a circular buffer mode. Unlike the +"multi" mode, it will fill out all the windows in the buffer as opposed +to just the first one. It can be enabled by writing "sink" to the "mode" +file (assuming msu-sink.ko is loaded). |