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    Subject[PATCH V2 0/5] trace-cmd: Support the feature recording trace data of guests on the host
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    Hi Steven,

    This is a v2 patch set for realizing a part of "Integrated trace" feature which
    is a trace merging system for a virtualization environment. Currently, trace-cmd
    does not have following features yet:

    a) Server and client for a virtualization environment
    b) Structured message platform between guests and host
    c) Agent feature of a client
    d) Merge feature of trace data of multiple guests and host in chronological
    order

    This patch set supports above a) and b) features.

    <overall view>

    +------------+ +------------+
    Guest | a), c) | | a), c) | client/agent
    ^ +------------+ +------------+
    | ^ ^ ^ ^
    ============|===|=================|===|===========
    | v b)v v b)v
    v +----------------------------------+
    Host | a) | server
    +----------------------------------+
    ||output || ||
    \/ \/ \/
    /--------+ /--------+ /--------+
    | 010101 | | 101010 | | 100101 | binary data
    | 010100 | | 010100 | | 110011 |
    +--------+ +--------+ +--------+
    \ /
    \-----------------------------------/
    || d)
    \/
    /-----------------------------------+
    | (guest1) 123456: sched_switch... | text data
    | (guest2) 123458: kmem_free... |
    | (host) 123500: kvm_exit (guest1)|
    | (host) 123510: kvm_entry(guest1)|
    | (guest1) 123550: sched_switch... |
    +-----------------------------------+

    a) Server and client for a virtualization environment
    trace-cmd has listen mode for network, but using network will be a high cost
    operation for inducing a lot of memory copying. From kernel-3.6, the
    virtio-console driver supports splice_write and ftrace supports "steal" for
    fops. So, guest clients of trace-cmd can send trace data without copying memory
    by using splice(2). If guest clients use virtio-serial, the server also needs to
    support virtio-serial I/F.

    b) Structured message platform between guests and a host
    Currently, a server(clients) sends unstructured character string to
    clients(server), so clients(server) must parse the unstructured messages.
    Since it is hard to add complex contents in the protocol, structured binary
    message trace-msg is introduced as the communication protocol.

    c) Agent feature of a client
    Current trace-cmd client can operate only as "record" mode, so the client
    will send trace data to the server immediately. However, when an user tries to
    collect trace data of multiple guests on a host, the user must log in to
    each guest. This is hard to use, I think. So, trace-cmd client had better
    support agent mode which receives a message from the server.

    d) Merge feature of trace data of multiple guests and a host in chronological
    order
    Current trace-cmd has a merge feature for multiple machines whose times are
    synchronized by NTP. When we use the feature, we execute "trace-cmd record"
    with --date option on each machine, and then we run "trace-cmd report" with -i
    option for each file.
    However, there are cases that times of those machines cannot be synchronized.
    For example, although multiple users can run guests on virtualization
    environments (e.g. multi-tenant cloud hosting), there are no guarantee that
    they use the same NTP server. Moreover, even if the times are synchronized,
    trace data cannot exactly be merged because the NTP-synchronized time
    granularity may not be enough fine for sorting guest-host switching events.
    So, I'm considering that trace data use x86-tsc as timestamp in order to merge
    trace data. By using x86-tsc, we can merge trace data even if time of those
    machines is not synchronized when CPU has the invariant TSC feature or the
    constant TSC feature. And the precision will be enough for understanding
    operations of guests and host. However, TSC values on a guest are not equal to
    the values on the host because
    TSC_guest = TSC_host + TSC_offset.
    This series actually doesn't support TSC offset, but I'd like to add such
    feature to fix host/guest clock difference in the other series. TSC offset
    values can be gotten as write_tsc_offset trace event from kernel-3.11.
    (see https://lkml.org/lkml/2013/6/12/72)

    For a), this patch introduces "virt-server" and "record --virt" modes for
    achieving low-overhead communication of trace data of guests. "virt-server" is a
    server mode for collecting trace data of guests. On the other hand,
    "record --virt" mode is a guest client for sending trace data of the guest.
    Although these functions are similar to "listen" and "record -N" modes each,
    these do not use network but use virtio-serial for low-overhead communication.

    For b), this patch series introduce specific message protocol in order to handle
    communication messages with 8 commands. When we extend any messages, using
    structured message will be easier than using unstructured message.

    <How to use>
    1. Run virt-server on a host
    # trace-cmd virt-server

    2. Make guest domain directory
    # mkdir -p /tmp/trace-cmd/virt/<domain>
    # chmod 710 /tmp/trace-cmd/virt/<domain>
    # chgrp qemu /tmp/trace-cmd/virt/<domain>

    3. Make FIFO on the host
    # mkfifo /tmp/trace-cmd/virt/<domain>/trace-path-cpu{0,1,...,X}.{in,out}

    4. Set up of virtio-serial pipe of a guest on the host
    Add the following tags to domain XML files.
    # virsh edit <domain>
    <channel type='unix'>
    <source mode='connect' path='/tmp/trace-cmd/virt/agent-ctl-path'/>
    <target type='virtio' name='agent-ctl-path'/>
    </channel>
    <channel type='pipe'>
    <source path='/tmp/trace-cmd/virt/<domain>/trace-path-cpu0'/>
    <target type='virtio' name='trace-path-cpu0'/>
    </channel>
    ... (cpu1, cpu2, ...)

    5. Boot the guest
    # virsh start <domain>

    6. Execute "record --virt" on the guest
    # trace-cmd record --virt -e sched*

    <Result>
    I measured CPU usage outputted by top command on a guest when client sends
    trace data. Client means "record -N"(NW) or "record --virt"(virtio-serial).

    NW virtio-serial(splice)
    client(fedora19) ~2.9[%] ~1.7[%]

    <Future work>
    - Add an agent mode based on "record --virt"
    - Add a merging feature of trace data of guests and host to "report"

    Changes in V2:
    [1/5] Add a comment in open_udp()
    [2/5] Regacy protocol support in order to keep backward compatibility

    Thank you,

    ---

    Yoshihiro YUNOMAE (5):
    [CLEANUP] trace-cmd: Split out binding a port and fork reader from open_udp()
    trace-cmd: Apply the trace-msg protocol for communication between a server and clients
    trace-cmd: Use poll(2) to wait for a message
    trace-cmd: Add virt-server mode for a virtualization environment
    trace-cmd: Add --virt option for record mode


    Documentation/trace-cmd-record.1.txt | 11
    Documentation/trace-cmd-virt-server.1.txt | 89 +++
    Makefile | 2
    trace-cmd.c | 3
    trace-cmd.h | 14
    trace-listen.c | 601 ++++++++++++++++----
    trace-msg.c | 874 +++++++++++++++++++++++++++++
    trace-msg.h | 31 +
    trace-output.c | 4
    trace-record.c | 146 ++++-
    trace-recorder.c | 54 +-
    trace-usage.c | 10
    12 files changed, 1678 insertions(+), 161 deletions(-)
    create mode 100644 Documentation/trace-cmd-virt-server.1.txt
    create mode 100644 trace-msg.c
    create mode 100644 trace-msg.h

    --
    Yoshihiro YUNOMAE
    Software Platform Research Dept. Linux Technology Center
    Hitachi, Ltd., Yokohama Research Laboratory
    E-mail: yoshihiro.yunomae.ez@hitachi.com


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