Feedback requested on switching the exception wrapper used for the PMU interrupt on ppc64

[Corey J Ashford]

Just FYI:  I just tried out the code I suggested below, and it does not
work; it results in a system hang.  I have spent some time analyzing why
this doesn't work as I expected, but so far I haven't been able to figure
it out.

Regards,

Corey Ashford
Software Engineer
IBM Linux Technology Center, Linux Toolchain
Beaverton, OR
503-578-3507
cjashfor at us.ibm.com


linuxppc-dev-bounces+cjashfor=us.ibm.com at ozlabs.org wrote on 05/15/2008
12:41:55 PM:

> Hi Benjamin and Olaf,
>
> Thanks for the suggestions.
>
> Ideally, what I'm looking for is something that mimics the operation
> of MASKABLE_EXCEPTION_PSERIES.
> I've been looking at the kernel code (entry_64.S, exception.h,
> head_64.S) but am finding it quite complicated and hard to follow,
> particularly in the area of interrupt disabling wrt the soft and
> hard disable logic.
>
> My initial thought is to do something like this in the beginning of
> my perfmon2 interrupt handler:
>
> void perfmon_pmu_int_handler(struct pt_regs *regs) {
>
> if (get_paca()->soft_enabled == 0) {
> /* disable hardware interrupts */
> get_paca()->hard_enabled = 0;
> regs->msr &= ^MSR_EE;
> return;
> }
> ...
> }
>
> Does this seem like it might work?
>
> Thanks
>
> Corey Ashford
> Software Engineer
> IBM Linux Technology Center, Linux Toolchain
> Beaverton, OR
> 503-578-3507
> cjashfor at us.ibm.com
>
>
> Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on
> 05/14/2008 11:46:07 PM:
>
> >
> > On Tue, 2008-05-13 at 15:26 -0700, Corey Ashford wrote:
> > > The perfmon2 code is available here:
> > > http://sourceforge.net/project/showfiles.php?group_id=144822
> > >
> > > perfmon2's interrupt handler does have a single entry point.  Could I

> > > somehow mimic what the MASKABLE_EXCEPTION_PSERIES macro does inside
> > > of
> > > the perfmon2 interrupt handler?  Are there examples of this I can
look
> > > at?
> > >
> > > That would give us the best of both worlds.
> >
> > You can definitely snapshot as many data as you can, and if interrupts
> > are soft-disabled, just return to the caller, storing that snapshot in
> > some per-cpu data structure.
> >
> > You can then add something to local_irq_restore() that checks whether
> > some perfmon2 stuff happened and does the actual storing of the data
> > that were previously collected.
> >
> > Cheers,
> > Ben.
> >
> > _______________________________________________
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> Linuxppc-dev at ozlabs.org
> https://ozlabs.org/mailman/listinfo/linuxppc-dev
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