Re: Oops with oprofile + RT preempt 2.6.11-rc2-RT-V0.7.37-01

From: Ingo Molnar (mingo_at_elte.hu)
Date: 02/17/05

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    Date:	Thu, 17 Feb 2005 21:11:45 +0100
To: Lee Revell <rlrevell@joe-job.com>

    * Lee Revell <rlrevell@joe-job.com> wrote:

    > I noticed profiling the kernel with PREEMPT_DESKTOP that mcount and
    > __mcount add quite a bit of overhead. Something like .5% CPU each.
    > Sorry, I didn't save the oprofile output.
    >
    > So, disable CONFIG_MCOUNT if you want minimal overhead from the RT
    > patches. IIRC it was previously stated that the latency tracing
    > overhead could be mostly avoided by disabling it at runtime.

    yes - most of the overhead can be disabled, but not all. 1% CPU time
    might sound alot but when compared against 10% (or more) tracing
    overehad it's small. The least overhead comes from disabling tracing in
    the .config.

            Ingo
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