* Don Zickus <[email protected]> wrote:
> I noticed when debugging a perf problem on a machine with GHES enabled,
> perf seemed slow. I then realized that the GHES NMI routine was taking
> a global lock all the time to inspect the hardware. This contended
> with all the local perf counters which did not need a lock. So each cpu
> accidentally was synchronizing with itself when using perf.
>
> This is because the way the nmi handler works. It executes all the handlers
> registered to a particular subtype (to deal with nmi sharing). As a result
> the GHES handler was executed on every PMI.
>
> Fix this by creating a new nmi type called NMI_EXT, which is used by
> handlers that need to probe external hardware and require a global lock
> to do so.
>
> Now the main NMI handler can check the internal NMI handlers first and
> then the external ones if nothing is found.
>
> This makes perf a little faster again on those machines with GHES enabled.
So what happens if GHES asserts an NMI at the same time a PMI
triggers?
If the perf PMI executes and indicates that it has handled something,
we don't execute the GHES handler, right? Will the GHES re-trigger the
NMI after we return?
Thanks,
Ingo
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