v8 changes: - Call delayed_uprobe_remove(uprobe, NULL) from put_uprobe() as well. - Other minor optimizations. v7: https://lkml.org/lkml/2018/7/31/20 Description: 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. Currently, perf tool has limited supports for SDT markers. I.e. it can not trace markers surrounded by reference counter. Also, it's not easy to add reference counter logic in userspace tool like perf, so basic idea for this patchset is to add reference counter logic in the a uprobe infrastructure. Ex,[2] # cat tick.c ... for (i = 0; i < 100; i++) { DTRACE_PROBE1(tick, loop1, i); if (TICK_LOOP2_ENABLED()) { DTRACE_PROBE1(tick, loop2, i); } printf("hi: %d\n", i); sleep(1); } ... Here tick:loop1 is marker without reference counter where as tick:loop2 is surrounded by reference counter condition. # perf buildid-cache --add /tmp/tick # perf probe sdt_tick:loop1 # perf probe sdt_tick:loop2 # perf stat -e sdt_tick:loop1,sdt_tick:loop2 -- /tmp/tick hi: 0 hi: 1 hi: 2 ^C Performance counter stats for '/tmp/tick': 3 sdt_tick:loop1 0 sdt_tick:loop2 2.747086086 seconds time elapsed Perf failed to record data for tick:loop2. Same experiment with this patch series: # ./perf buildid-cache --add /tmp/tick # ./perf probe sdt_tick:loop2 # ./perf stat -e sdt_tick:loop2 /tmp/tick hi: 0 hi: 1 hi: 2 ^C Performance counter stats for '/tmp/tick': 3 sdt_tick:loop2 2.561851452 seconds time elapsed [1] https://sourceware.org/systemtap/wiki/UserSpaceProbeImplementation Ravi Bangoria (6): Uprobes: Simplify uprobe_register() body Uprobe: Additional argument arch_uprobe to uprobe_write_opcode() Uprobes: Support SDT markers having reference count (semaphore) Uprobes/sdt: Prevent multiple reference counter for same uprobe trace_uprobe/sdt: Prevent multiple reference counter for same uprobe perf probe: Support SDT markers having reference counter (semaphore) arch/arm/probes/uprobes/core.c | 2 +- arch/mips/kernel/uprobes.c | 2 +- include/linux/uprobes.h | 7 +- kernel/events/uprobes.c | 329 +++++++++++++++++++++++++++++++++++------ kernel/trace/trace.c | 2 +- kernel/trace/trace_uprobe.c | 75 +++++++++- tools/perf/util/probe-event.c | 39 ++++- tools/perf/util/probe-event.h | 1 + tools/perf/util/probe-file.c | 34 ++++- tools/perf/util/probe-file.h | 1 + tools/perf/util/symbol-elf.c | 46 ++++-- tools/perf/util/symbol.h | 7 + 12 files changed, 472 insertions(+), 73 deletions(-) -- 2.14.4
