Commit e64dd5ef authored by Eiichi Tsukata's avatar Eiichi Tsukata Committed by Stefan Hajnoczi
Browse files

trace: document ftrace backend 



Add documentation of ftrace backend.

Signed-off-by: default avatarEiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 781e9545

docs/tracing.txt

+16 −0
Original line number Diff line number Diff line
@@ -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>