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Re: [Qemu-devel] [PATCH v2 0/2] New trace backend: ftrace
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/2] New trace backend: ftrace |
Date: |
Fri, 12 Apr 2013 13:06:21 +0200 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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