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SubjectRe: [PATCH] x86: Document the hotplug code is incompatible with x86 irq handling
On Tuesday, 12 June 2007 23:56, Siddha, Suresh B wrote:
> On Tue, Jun 12, 2007 at 10:52:09PM +0200, Rafael J. Wysocki wrote:
> > On Tuesday, 12 June 2007 20:19, Eric W. Biederman wrote:
> > > Because you are calling unfixably broken code. That should be a decent
> > > incentive to do something else won't it?
> >
> > Can you please tell me _what_ else can be done?
> >
> > > IOAPICs do not support what the code is doing here. There is lots of
> > > practical evidence including bad experiences and practical tests that
> > > support this.
> >
> > Well, AFAICS, Suresh has tried to debug one failing case recently without
> > any consistent conclusions. I don't know of any other test cases (links,
> > please?).
> Rafael, Darrick Wong's issue looks different and hence I was motivated to
> look and fix if it was a SW issue. For now, I am not able to comprehend
> what is happening on Darrick Wong's system. Need more help from Darrick
> as he has the golden failing system.
> Meanwhile I talked to our hardware folks about the irq migration in general.
> One good news is that future versions of chipsets will have an Interrupt
> Remapping feature(for more details please refer to
> where in we can reliably migrate the irq to someother cpu in the process
> context.
> And for the existing platforms, chipset folks don't see a reason why the
> Eric's algorithm(specified below) should fail.
> Eric's algorithm for level triggered(edge triggered should be easier than
> level triggered):
> - Mask the irq in process context.
> - Poll RIRR until an ack of for the irq was not pending.
> - Migrate the irq.
> Eric had a problem of stuck remote IRR on E75xx chipset with this algorithm
> and my next step is to reproduce this issue on this platform and understand
> the behavior.


In that case, do I understand correctly that we are going to implement the
Eric's algorithm above for the CPU hotunplugging on x86 once you've figured
out what's the E75xx issue?


"Premature optimization is the root of all evil." - Donald Knuth
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