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trace: document ftrace backend 

Add documentation of ftrace backend.

Signed-off-by: Eiichi Tsukata <eiichi.tsukata.xh@hitachi.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Eiichi Tsukata 2013-04-11 20:25:16 +09:00 committed by Stefan Hajnoczi
parent 781e9545db
commit e64dd5efb2
1 changed files with 16 additions and 0 deletions
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docs/tracing.txt
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@ -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>