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Diffstat (limited to 'Documentation/trace/intel_th.rst')
| -rw-r--r-- | Documentation/trace/intel_th.rst | 28 |
1 files changed, 27 insertions, 1 deletions
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). |