Re: [PATCH 4/6] trace: trace syscall in its handler not from ptracehandler

From: H. Peter Anvin
Date: Thu Mar 29 2012 - 15:13:15 EST

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.


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

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