Re: dom0 kernel profiling on Xen

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Apr 11, 2016 at 12:34:30PM +0200, Manuel Bouyer wrote:
> [...]
> it seems that __cpu_simple_lock doens't call mcount.
> Now I have to find why this doens't loop on bare metal. Any idea before
> I keep looking ?

The __cpu_simple_unlock function is the same in GENERIC and XEN3_DOM*.

The difference is the x86_lfence call, this comes from 
mcount_disable_intr() and mcount_write_psl() (via MCOUNT_ENTER/MCOUNT_EXIT)
which are different for Xen. I inlined an lfence instruction in mcount_*
instead of calling x86_lfence and now I don't get the stack overflow.

I get a hard hang, it seems that interrupts are not re-enabled.
*But* I get the same hard hang with GENERIC, so it seems that profiling
is generally broken (at last on amd64) in HEAD these days.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
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