^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) Trace Agent for virtio-trace
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) ============================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) Trace agent is a user tool for sending trace data of a guest to a Host in low
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) overhead. Trace agent has the following functions:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) - splice a page of ring-buffer to read_pipe without memory copying
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) - splice the page from write_pipe to virtio-console without memory copying
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) - write trace data to stdout by using -o option
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) - controlled by start/stop orders from a Host
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) The trace agent operates as follows:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) 1) Initialize all structures.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) 2) Create a read/write thread per CPU. Each thread is bound to a CPU.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) The read/write threads hold it.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) 3) A controller thread does poll() for a start order of a host.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) 4) After the controller of the trace agent receives a start order from a host,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) the controller wake read/write threads.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) 5) The read/write threads start to read trace data from ring-buffers and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) write the data to virtio-serial.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) 6) If the controller receives a stop order from a host, the read/write threads
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) stop to read trace data.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) Files
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) =====
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) README: this file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) Makefile: Makefile of trace agent for virtio-trace
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) trace-agent.c: includes main function, sets up for operating trace agent
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) trace-agent.h: includes all structures and some macros
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) trace-agent-ctl.c: includes controller function for read/write threads
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) trace-agent-rw.c: includes read/write threads function
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) Setup
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) =====
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) To use this trace agent for virtio-trace, we need to prepare some virtio-serial
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) I/Fs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) 1) Make FIFO in a host
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) virtio-trace uses virtio-serial pipe as trace data paths as to the number
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) of CPUs and a control path, so FIFO (named pipe) should be created as follows:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) # mkdir /tmp/virtio-trace/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) # mkfifo /tmp/virtio-trace/trace-path-cpu{0,1,2,...,X}.{in,out}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) # mkfifo /tmp/virtio-trace/agent-ctl-path.{in,out}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) For example, if a guest use three CPUs, the names are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) trace-path-cpu{0,1,2}.{in.out}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) agent-ctl-path.{in,out}.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) 2) Set up of virtio-serial pipe in a host
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) Add qemu option to use virtio-serial pipe.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) ##virtio-serial device##
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) -device virtio-serial-pci,id=virtio-serial0\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) ##control path##
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) -chardev pipe,id=charchannel0,path=/tmp/virtio-trace/agent-ctl-path\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) -device virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) id=channel0,name=agent-ctl-path\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) ##data path##
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) -chardev pipe,id=charchannel1,path=/tmp/virtio-trace/trace-path-cpu0\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) -device virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel0,\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) id=channel1,name=trace-path-cpu0\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) ...
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) If you manage guests with libvirt, add the following tags to domain XML files.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) Then, libvirt passes the same command option to qemu.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) <channel type='pipe'>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) <source path='/tmp/virtio-trace/agent-ctl-path'/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) <target type='virtio' name='agent-ctl-path'/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) <address type='virtio-serial' controller='0' bus='0' port='0'/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) </channel>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) <channel type='pipe'>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) <source path='/tmp/virtio-trace/trace-path-cpu0'/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) <target type='virtio' name='trace-path-cpu0'/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) <address type='virtio-serial' controller='0' bus='0' port='1'/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) </channel>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) ...
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) Here, chardev names are restricted to trace-path-cpuX and agent-ctl-path. For
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) example, if a guest use three CPUs, chardev names should be trace-path-cpu0,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) trace-path-cpu1, trace-path-cpu2, and agent-ctl-path.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) 3) Boot the guest
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) You can find some chardev in /dev/virtio-ports/ in the guest.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) Run
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) ===
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93) 0) Build trace agent in a guest
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) $ make
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) 1) Enable ftrace in the guest
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) <Example>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) # echo 1 > /sys/kernel/debug/tracing/events/sched/enable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) 2) Run trace agent in the guest
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) This agent must be operated as root.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) # ./trace-agent
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) read/write threads in the agent wait for start order from host. If you add -o
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) option, trace data are output via stdout in the guest.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) 3) Open FIFO in a host
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) # cat /tmp/virtio-trace/trace-path-cpu0.out
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) If a host does not open these, trace data get stuck in buffers of virtio. Then,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) the guest will stop by specification of chardev in QEMU. This blocking mode may
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) be solved in the future.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) 4) Start to read trace data by ordering from a host
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) A host injects read start order to the guest via virtio-serial.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) # echo 1 > /tmp/virtio-trace/agent-ctl-path.in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) 5) Stop to read trace data by ordering from a host
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) A host injects read stop order to the guest via virtio-serial.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) # echo 0 > /tmp/virtio-trace/agent-ctl-path.in
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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