Hello Steven, On 07/24/2018 04:25 PM, Steven Rostedt wrote: > On Tue, 24 Jul 2018 10:23:16 -0400 > Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > >>> >>> Would work in the direction of adding a global trace_pipe_raw be considered >>> for inclusion? >> >> The design of the lockless ring buffer requires not to be preempted, >> and that the data cannot be written to from more than one location. To >> do so, we make a per CPU buffer, and disable preemption when writing. >> This means that we have only one writer at a time. It can handle >> interrupts and NMIs, because they will finish before they return and >> this doesn't break the algorithm. But having writers from multiple CPUs >> would require locking or other heaving synchronization operations that >> will greatly reduce the speed of writing to the buffers (not to mention >> the cache thrashing). > > And why would you need a single buffer? Note, we are working on making > libtracecmd.so that will allow applications to read the buffers and the > library will take care of the interleaving of the raw data. This should > hopefully be ready in about three months or so. > > -- Steve > Is this something you will showcase in the linux tracing summit? Is there a repo / branch I should be following? The reason why we need to end up with a single stream of events is to be able to do "online" task state correlation and timing parameters calculations for all task-related events independent of cores. Currently we have this on QNX, and we are trying to enable it for Linux as well. Thank you, Claudio
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