linux-kernel - Re: [RESEND PATCH] perf/x86/intel: Fix unchecked MSR access error for Alder Lake N

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Message-ID: <Yv9EVP6O9r867om4@worktop.programming.kicks-ass.net>
Date:   Fri, 19 Aug 2022 10:05:40 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kan.liang@...ux.intel.com
Cc:     acme@...hat.com, linux-kernel@...r.kernel.org,
        alexander.shishkin@...ux.intel.com, ak@...ux.intel.com,
        Jianfeng Gao <jianfeng.gao@...el.com>
Subject: Re: [RESEND PATCH] perf/x86/intel: Fix unchecked MSR access error
 for Alder Lake N

On Thu, Aug 18, 2022 at 11:15:30AM -0700, kan.liang@...ux.intel.com wrote:

> The Alder Lake N only has e-cores. The X86_FEATURE_HYBRID_CPU flag is
> not set. The perf cannot retrieve the correct CPU type via
> get_this_hybrid_cpu_type(). The model specific get_hybrid_cpu_type() is
> hardcode to p-core. The wrong CPU type is given to the PMU of the
> Alder Lake N.

If ADL-N isn't in fact a hybrid CPU, then *WHY* are we running
init_hybrid_pmu() and setting up all that nonsense?

That is, wouldn't the right thing be to remove ALDERLAKE_N from the rest
of {ALDER,RAPTOP}LAKE and create a non-hybrid PMU setup for it?