[4/4] trace: document ftrace backend

Submitted by Stefan Hajnoczi on May 3, 2013, 12:01 p.m.


Message ID 1367582485-15579-5-git-send-email-stefanha@redhat.com
State New
Headers show

Commit Message

Stefan Hajnoczi May 3, 2013, 12:01 p.m.
From: Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>

Add documentation of ftrace backend.

Signed-off-by: Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
 docs/tracing.txt | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

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diff --git a/docs/tracing.txt b/docs/tracing.txt
index cf53c17..60ff9c5 100644
--- a/docs/tracing.txt
+++ b/docs/tracing.txt
@@ -175,6 +175,22 @@  unless you have specific needs for more advanced backends.
 The "simple" backend currently does not capture string arguments, it simply
 records the char* pointer value instead of the string that is pointed to.
+=== Ftrace ===
+The "ftrace" backend writes trace data to ftrace marker. This effectively
+sends trace events to ftrace ring buffer, and you can compare qemu trace
+data and kernel(especially kvm.ko when using KVM) trace data.
+if you use KVM, 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
+Restriction: "ftrace" backend is restricted to Linux only.
 ==== Monitor commands ====
 * trace-file on|off|flush|set <path>