On Thu, Apr 11, 2013 at 08:25:14PM +0900, Eiichi Tsukata wrote: > This patchset introduces a new tracing backend "ftrace". > > Currently, QEMU tracing backends do not support userspace tracing with ftrace. > Collecting QEMU trace data and kernel trace data simultaneouly is useful for > latency analysis and debugging especially when using KVM. > > With ftrace backend, you can easily collect QEMU-kernel merged trace data > using existing ftrace event-based tracer. If you use KVM, you can effectively > compare VM_EXIT and QEMU userspace handler. > > To try it out, compile QEMU with tracing backend ftrace, then enable KVM > events > in ftrace: > > # echo 1 > /sys/kernel/debug/tracing/events/kvm/enable > > After running qemu by root user, you can get the trace: > > # cat /sys/kernel/debug/tracing/trace > > Example: > # tracer: nop > # > # entries-in-buffer/entries-written: 8434/345512 #P:4 > # > # _-----=> irqs-off > # / _----=> need-resched > # | / _---=> hardirq/softirq > # || / _--=> preempt-depth > # ||| / delay > # TASK-PID CPU# |||| TIMESTAMP FUNCTION > # | | | |||| | | > <snip> > qemu-system-x86-31930 [000] d... 23580.595951: kvm_exit: reason > IO_INSTRUCTION rip 0xc45d info 710048 0 > qemu-system-x86-31930 [000] .... 23580.595954: kvm_emulate_insn: > f0000:c45d:e4 71 (real) > qemu-system-x86-31930 [000] .... 23580.595955: kvm_pio: pio_read at 0x71 > size 1 count 1 > qemu-system-x86-31930 [000] .... 23580.595956: kvm_userspace_exit: reason > KVM_EXIT_IO (2) > qemu-system-x86-31930 [000] ...1 23580.595959: tracing_mark_write: > cpu_set_apic_base 00000000fee00900 > qemu-system-x86-31930 [000] ...1 23580.595961: tracing_mark_write: cpu_in > addr 0x71 value 0 > qemu-system-x86-31930 [000] d... 23580.595964: kvm_entry: vcpu 0 > <snip> > > "tracing_mark_write: cpu_set_apic_base 00000000fee00900" and > "tracing_mark_write: cpu_in addr 0x71 value 0" are QEMU trace data. > Others are Kernel trace data. > > Furthermore, the ftrace backend overhead is smaller than uprobe-based event > tracer or SystemTap. My microbenchmark shows that ftrace tracing backend > overhead is about 0.8us per tracepoint, whereas uprobe-based event tracer > or SystemTap overhead is about 2.0us. > > Changes in v2: > * fix Stefan's mail address. > * use snprintf return value not to waste trace buffer. > > Eiichi Tsukata (2): > trace: Add ftrace tracing backend > trace: document ftrace backend > > configure | 8 +++ > docs/tracing.txt | 16 ++++++ > scripts/tracetool/backend/ftrace.py | 54 +++++++++++++++++++ > trace/Makefile.objs | 1 + > trace/ftrace.c | 102 > ++++++++++++++++++++++++++++++++++++ > trace/ftrace.h | 10 ++++ > 6 files changed, 191 insertions(+) > create mode 100644 scripts/tracetool/backend/ftrace.py > create mode 100644 trace/ftrace.c > create mode 100644 trace/ftrace.h > > -- > 1.8.1.4 > >
Thanks, applied to my tracing tree: https://github.com/stefanha/qemu/commits/tracing Stefan
