Add events to enumerate kernel symbols #21
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This adds an event for each kernel symbol during statedump. It uses the kallsyms_on_each_symbol kernel function to go through all available symbols. Going through the symbols adds a fixed cost to the statedump (9ms on a machine where statedump usually takes 20ms, so the overhead for the statedump is slightly lower than 50%) when tracepoints are _not_ enabled. With the symbol tracepoints enabled, it adds ~135 000 events and more than doubles the time of the statedump (adds 35ms, so an overhead of 175% compared to statedump without the symbols). It may cause lost events with the default channel value since the event rate is very dense during that time. A trace with only the kernel symbol events has a size of ~5MB on a normal desktop. In comparison the /proc/kallsyms fils has 6MB. Signed-off-by: Geneviève Bastien <[email protected]>
Add tracepoints to enumerate the new symbols brought when a new kernel module is loaded. It uses the kallsyms_on_each_symbol and filters the symbols from the new module, as this function is the one exported from the kernel to list the symbols. It has the same fixed cost from the function itself (~9ms), whether events are enabled or not. When the module is unloaded, there is only one event to notify of the module unload. Signed-off-by: Geneviève Bastien <[email protected]>
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To load the new probe automatically in session daemon, see the following PR of lttng-tools: lttng/lttng-tools#153 |
compudj
requested changes
Jun 19, 2019
compudj
requested changes
Jun 19, 2019
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Will make a new PR |
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The kernel symbols in the trace allow to resolve function pointers automatically from the trace's data. This can be useful for events having function pointers as fields, like timers, or the callstack-kernel context which lists the kernel addresses of the current callstack.
Details on overhead and event count can be found in the specific commits.