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author | André Fabian Silva Delgado <emulatorman@parabola.nu> | 2015-08-05 17:04:01 -0300 |
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committer | André Fabian Silva Delgado <emulatorman@parabola.nu> | 2015-08-05 17:04:01 -0300 |
commit | 57f0f512b273f60d52568b8c6b77e17f5636edc0 (patch) | |
tree | 5e910f0e82173f4ef4f51111366a3f1299037a7b /tools/virtio/virtio-trace/README |
Initial import
Diffstat (limited to 'tools/virtio/virtio-trace/README')
-rw-r--r-- | tools/virtio/virtio-trace/README | 118 |
1 files changed, 118 insertions, 0 deletions
diff --git a/tools/virtio/virtio-trace/README b/tools/virtio/virtio-trace/README new file mode 100644 index 000000000..b64845b82 --- /dev/null +++ b/tools/virtio/virtio-trace/README @@ -0,0 +1,118 @@ +Trace Agent for virtio-trace +============================ + +Trace agent is a user tool for sending trace data of a guest to a Host in low +overhead. Trace agent has the following functions: + - splice a page of ring-buffer to read_pipe without memory copying + - splice the page from write_pipe to virtio-console without memory copying + - write trace data to stdout by using -o option + - controlled by start/stop orders from a Host + +The trace agent operates as follows: + 1) Initialize all structures. + 2) Create a read/write thread per CPU. Each thread is bound to a CPU. + The read/write threads hold it. + 3) A controller thread does poll() for a start order of a host. + 4) After the controller of the trace agent receives a start order from a host, + the controller wake read/write threads. + 5) The read/write threads start to read trace data from ring-buffers and + write the data to virtio-serial. + 6) If the controller receives a stop order from a host, the read/write threads + stop to read trace data. + + +Files +===== + +README: this file +Makefile: Makefile of trace agent for virtio-trace +trace-agent.c: includes main function, sets up for operating trace agent +trace-agent.h: includes all structures and some macros +trace-agent-ctl.c: includes controller function for read/write threads +trace-agent-rw.c: includes read/write threads function + + +Setup +===== + +To use this trace agent for virtio-trace, we need to prepare some virtio-serial +I/Fs. + +1) Make FIFO in a host + virtio-trace uses virtio-serial pipe as trace data paths as to the number +of CPUs and a control path, so FIFO (named pipe) should be created as follows: + # mkdir /tmp/virtio-trace/ + # mkfifo /tmp/virtio-trace/trace-path-cpu{0,1,2,...,X}.{in,out} + # mkfifo /tmp/virtio-trace/agent-ctl-path.{in,out} + +For example, if a guest use three CPUs, the names are + trace-path-cpu{0,1,2}.{in.out} +and + agent-ctl-path.{in,out}. + +2) Set up of virtio-serial pipe in a host + Add qemu option to use virtio-serial pipe. + + ##virtio-serial device## + -device virtio-serial-pci,id=virtio-serial0\ + ##control path## + -chardev pipe,id=charchannel0,path=/tmp/virtio-trace/agent-ctl-path\ + -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,\ + id=channel0,name=agent-ctl-path\ + ##data path## + -chardev pipe,id=charchannel1,path=/tmp/virtio-trace/trace-path-cpu0\ + -device virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel0,\ + id=channel1,name=trace-path-cpu0\ + ... + +If you manage guests with libvirt, add the following tags to domain XML files. +Then, libvirt passes the same command option to qemu. + + <channel type='pipe'> + <source path='/tmp/virtio-trace/agent-ctl-path'/> + <target type='virtio' name='agent-ctl-path'/> + <address type='virtio-serial' controller='0' bus='0' port='0'/> + </channel> + <channel type='pipe'> + <source path='/tmp/virtio-trace/trace-path-cpu0'/> + <target type='virtio' name='trace-path-cpu0'/> + <address type='virtio-serial' controller='0' bus='0' port='1'/> + </channel> + ... +Here, chardev names are restricted to trace-path-cpuX and agent-ctl-path. For +example, if a guest use three CPUs, chardev names should be trace-path-cpu0, +trace-path-cpu1, trace-path-cpu2, and agent-ctl-path. + +3) Boot the guest + You can find some chardev in /dev/virtio-ports/ in the guest. + + +Run +=== + +0) Build trace agent in a guest + $ make + +1) Enable ftrace in the guest + <Example> + # echo 1 > /sys/kernel/debug/tracing/events/sched/enable + +2) Run trace agent in the guest + This agent must be operated as root. + # ./trace-agent +read/write threads in the agent wait for start order from host. If you add -o +option, trace data are output via stdout in the guest. + +3) Open FIFO in a host + # cat /tmp/virtio-trace/trace-path-cpu0.out +If a host does not open these, trace data get stuck in buffers of virtio. Then, +the guest will stop by specification of chardev in QEMU. This blocking mode may +be solved in the future. + +4) Start to read trace data by ordering from a host + A host injects read start order to the guest via virtio-serial. + # echo 1 > /tmp/virtio-trace/agent-ctl-path.in + +5) Stop to read trace data by ordering from a host + A host injects read stop order to the guest via virtio-serial. + # echo 0 > /tmp/virtio-trace/agent-ctl-path.in |