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    SubjectRe: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler
    On 03/29/2012 12:02 PM, Vaibhav Nagarnaik wrote:
    >
    > Thanks for the feedback. I had missed this added latency due to this
    > patch when tracing is disabled.
    >
    > To fix that, instead of a TIF flag, I am using a flag in the
    > current->trace bitmap. I check that flag before jumping to the tracing
    > function. That reduces the latency from 83 ns/call to 74 ns/call.
    >

    ANY increase to the fastpath is unacceptable, period.

    Furthermore, as I have discussed with some people over the last few
    days, I think we should consider the whole syscall tracing interface set
    to be a mistake and deprecate it. There are much better ways to
    accomplish something that will work more reliable without all these thunks.

    -hpa

    --
    H. Peter Anvin, Intel Open Source Technology Center
    I work for Intel. I don't speak on their behalf.



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