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Conference turris::pca

Title:Notes Conference for VAX PCA
Notice:Current Version: V4.4-3 (see Note 2.1)
Moderator:EDSDS6::TOWNSEND
Created:Sat Jan 25 1986
Last Modified:Thu May 22 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:948
Total number of notes:3464

946.0. "Kernel questions" by INTONE::FONTAINE () Wed Mar 19 1997 15:37

I have looked through the current documentation and online
int his conference, and am having a hard time finding
definitive documentation regarding how PCA handles
kernel code. I found a note dated 28-JUN-1993 that states

"The restrictions on profiling elevated mode programs still apply"

Where is this documented? What happens if I have code that is
primarily in user space, but enters kernel space. How does
PCA handle this?

-Andre
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946.1not supportedEDSDS6::GLEASONDaryl Gleason, DECset EngineeringThu Mar 20 1997 10:2716
    Hi Andre,
    
    Note 615.1 in this conference has some summary information that may be
    helpful, but I don't think there is any documentation on exactly how
    PCA behaves apart from the statement that collection of data for kernel
    mode code (other than page fault data) is not supported. 
    
    Exactly what happens when such collection is attempted depends upon
    what data you're trying to collect. For example, if you're doing
    sampling, which is based upon a 10-millisecond timer, the timer ASTs
    cannot be delivered when kernel mode code is executing, so any pending
    sampling ASTs will be delivered all at once when the code returns to
    user mode (which obviously can skew the results if the code takes
    longer than 10ms to execute).
    
    -- Daryl
946.2What about coverage.INTONE::FONTAINEThu Mar 20 1997 17:075
What we are interested in is test coverage only. We're
curious about what happens in kernal mode when measuring
coverage.

-Andre
946.3EDSDS6::GLEASONDaryl Gleason, DECset EngineeringFri Mar 21 1997 08:2810
    In order to measure coverage, PCA needs to put a breakpoint in the code
    to be covered and subsequently trap it so that PCA can detect that the
    code has in fact been covered. Since PCA cannot trap breakpoints in
    kernel mode code, coverage data cannot be collected for that code.
    
    I'm not sure what the exact behavior might be if you try to do this;
    it's probably unpredictable. At any rate, I recommend that you avoid
    trying to collect coverage data on kernel mode code.
    
    -- Daryl
946.4Take alook at note #912.10SMURF::FENSTERYaacov Fenster - System Engineering, Troubleshooting and other mThu May 22 1997 19:185
    >                                           <<< Note 946.0 by INTONE::FONTAINE >>>
    >                                                   -< Kernel questions >-
    
    Take a look at note 912.10