Re: [PATCH 5/9] HWPoison: add memory_failure_queue()

[Ingo Molnar]

* huang ying <huang.ying.caritas@xxxxxxxxx> wrote:

> On Fri, May 20, 2011 at 7:56 PM, Ingo Molnar <mingo@xxxxxxx> wrote:
> >
> > * Huang Ying <ying.huang@xxxxxxxxx> wrote:
> >
> >> > So why are we not working towards integrating this into our event
> >> > reporting/handling framework, as i suggested it from day one on when you
> >> > started posting these patches?
> >>
> >> The memory_failure_queue() introduced in this patch is general, that is, it
> >> can be used not only by ACPI/APEI, but also any other hardware error
> >> handlers, including your event reporting/handling framework.
> >
> > Well, the bit you are steadfastly ignoring is what i have made clear well
> > before you started adding these facilities: THEY ALREADY EXISTS to a large
> > degree :-)
> >
> > So you were and are duplicating code instead of using and extending existing
> > event processing facilities. It does not matter one little bit that the code
> > you added is partly 'generic', it's still overlapping and duplicated.
> 
> How to do hardware error recovering in your perf framework?  IMHO, it can be 
> something as follow:
> 
> - NMI handler run for the hardware error, where hardware error
> information is collected and put into a ring buffer, an irq_work is
> triggered for further work
> - In irq_work handler, memory_failure_queue() is called to do the real
> recovering work for recoverable memory error in ring buffer.
> 
> What's your idea about hardware error recovering in perf?

The first step, the whole irq_work and ring buffer already looks largely 
duplicated: you can collect into a perf event ring-buffer from NMI context like 
the regular perf events do.

The generalization that *would* make sense is not at the irq_work level really, 
instead we could generalize a 'struct event' for kernel internal producers and 
consumers of events that have no explicit PMU connection.

This new 'struct event' would be slimmer and would only contain the fields and 
features that generic event consumers and producers need. Tracing events could 
be updated to use these kinds of slimmer events.

It would still plug nicely into existing event ABIs, would work with event 
filters, etc. so the tooling side would remain focused and unified.

Something like that. It is rather clear by now that splitting out irq_work was 
a mistake. But mistakes can be fixed and some really nice code could come out 
of it! Would you be interested in looking into this?

Thanks,

	Ingo
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