* Ravi Bangoria <[email protected]> [2018-08-20 10:12:47]: > Userspace Statically Defined Tracepoints[1] are dtrace style markers > inside userspace applications. Applications like PostgreSQL, MySQL, > Pthread, Perl, Python, Java, Ruby, Node.js, libvirt, QEMU, glib etc > have these markers embedded in them. These markers are added by developer > at important places in the code. Each marker source expands to a single > nop instruction in the compiled code but there may be additional > overhead for computing the marker arguments which expands to couple of > instructions. In case the overhead is more, execution of it can be > omitted by runtime if() condition when no one is tracing on the marker: > > if (reference_counter > 0) { > Execute marker instructions; > } > > Default value of reference counter is 0. Tracer has to increment the > reference counter before tracing on a marker and decrement it when > done with the tracing. > > Implement the reference counter logic in core uprobe. User will be > able to use it from trace_uprobe as well as from kernel module. New > trace_uprobe definition with reference counter will now be: > > <path>:<offset>[(ref_ctr_offset)] > > where ref_ctr_offset is an optional field. For kernel module, new > variant of uprobe_register() has been introduced: > > uprobe_register_refctr(inode, offset, ref_ctr_offset, consumer) > > No new variant for uprobe_unregister() because it's assumed to have > only one reference counter for one uprobe. > > [1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation > > Note: 'reference counter' is called as 'semaphore' in original Dtrace > (or Systemtap, bcc and even in ELF) documentation and code. But the > term 'semaphore' is misleading in this context. This is just a counter > used to hold number of tracers tracing on a marker. This is not really > used for any synchronization. So we are calling it a 'reference counter' > in kernel / perf code. >
Acked-by: Srikar Dronamraju <[email protected]> > Signed-off-by: Ravi Bangoria <[email protected]> > Reviewed-by: Masami Hiramatsu <[email protected]> > [Only trace_uprobe.c] > Reviewed-by: Oleg Nesterov <[email protected]> > ---
