[lkml]   [2009]   [May]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [RFC] convert ftrace syscall tracer to TRACE_EVENT()

    * Jason Baron <> wrote:

    > Hi,
    > I've been thinking about converting the current ftrace syscall
    > tracer to the TRACE_EVENT() macros. There are a few issues with
    > the current syscall tracer approach:
    > 1) It has to be enabled for all processes and all syscalls. By
    > moving to TRACE_EVENT(), it can be enabled/disabled per tracepoint
    > and can also make use of the generic tracing filters, such as
    > "trace all process for pid x"
    > 2) Other tracers can not tie into it, since its not tracepoint
    > based. TRACE_EVENT() fixes this.
    > 3) data formatting. The syscall tracer I don't believe understands
    > all the various types for output formatting. By moving to
    > TRACE_EVENT(), we can print out a more readible syscall trace.
    > 4) The ftrace syscall tracer needs a new arch specific code for
    > each architecture. By converting to TRACE_EVENT() we don't need
    > any architecutre specific code.
    > Other issues to consider:
    > * Maintainence. The current syscall tracer automatically picks up
    > new syscalls. The TRACE_EVENT() will be harder to initially set
    > up. But once its done, syscalls are obviously not added often. So
    > I don't think this will be too bad.
    > * Performance. The current syscall tracer adds a
    > 'test_thread_flag()' to syscall entry/exit. The TRACE_EVENT()
    > would add a per-syscall global to check. So they are going to have
    > different cache profiles...however, the tracepoint infrastructure
    > is hopefully moving to the 'immediate' value work, which will make
    > this more highly optimized.
    > I've also tested the patch shown below (which uses,
    > DECLARE_TRACE(), as a preliminary proof of concept), using
    > getpid() in a loop, and tbench, and saw very small performance
    > differences. Obviously we would have to do more extensive testing
    > before deciding.
    > Patch is pretty rough, but should give a rough sense of what the
    > DECLARE_TRACE() type patch might look like...

    Yeah, i very much agree with the direction. (I've Cc:-ed Tom Zanussi
    who also has expressed interest in this.)

    I'm not sure about the implementation as you've posted it though:

    Firstly, it adds two new tracepoints to every system call. That is
    unnecessary - we already have the TIF flag based callbacks, and we
    can use the existing syscall attributes table to get to tracepoints
    - without slow down (or impacting) the fast path in any way.

    Secondly, we should reuse the information we get in SYSCALL_DEFINE,
    to construct the TRACE_EVENT tracepoints directly - without having
    to list all syscalls again in a separate file.


     \ /
      Last update: 2009-05-09 10:41    [W:0.023 / U:45.172 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site