linux-kernel - Re: [PATCH] KVM: selftests: Test top-down slots event

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Date: Thu, 1 Feb 2024 10:02:47 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Kan Liang <kan.liang@...ux.intel.com>, Jim Mattson <jmattson@...gle.com>, 
	Jinrong Liang <cloudliang@...cent.com>, Aaron Lewis <aaronlewis@...gle.com>, 
	Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [PATCH] KVM: selftests: Test top-down slots event

On Thu, Feb 01, 2024, Dapeng Mi wrote:
> Although the fixed counter 3 and the exclusive pseudo slots events is
> not supported by KVM yet, the architectural slots event is supported by
> KVM and can be programed on any GP counter. Thus add validation for this
> architectural slots event.
> 
> Top-down slots event "counts the total number of available slots for an
> unhalted logical processor, and increments by machine-width of the
> narrowest pipeline as employed by the Top-down Microarchitecture
> Analysis method." So suppose the measured count of slots event would be
> always larger than 0.

Please translate that into something non-perf folks can understand.  I know what
a pipeline slot is, and I know a dictionary's definition of "available" is, but I
still have no idea what this event actually counts.  In other words, I want a
precise definition of exactly what constitutes an "available slot", in verbiage
that anyone with basic understanding of x86 architectures can follow after reading
the whitepaper[*], which is helpful for understanding the concepts, but doesn't
crisply explain what this event counts.

Examples of when a slot is available vs. unavailable would be extremely helpful.

[*] https://www.intel.com/content/www/us/en/docs/vtune-profiler/cookbook/2023-0/top-down-microarchitecture-analysis-method.html