linux-kernel - Re: [PATCH V2 03/14] x86/set_memory: Add x86_set_memory

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Message-ID: <fa63e6ad-9536-d5e9-d754-fa04fad69252@intel.com>
Date:   Thu, 5 Aug 2021 07:29:28 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Tianyu Lan <ltykernel@...il.com>
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Subject: Re: [PATCH V2 03/14] x86/set_memory: Add x86_set_memory_enc static
 call support

On 8/5/21 7:23 AM, Peter Zijlstra wrote:
> This is assuming any of this is actually performance critical, based off
> of this using static_call() to begin with.

This code is not performance critical.

I think I sent folks off on a wild goose chase when I asked that we make
an effort to optimize code that does:

	if (some_hyperv_check())
		foo();

	if (some_amd_feature_check())
		bar();

with checks that will actually compile away when Hyper-V or
some_amd_feature() is disabled.  That's less about performance and just
about good hygiene.  I *wanted* to see
cpu_feature_enabled(X86_FEATURE...) checks.

Someone suggested using static calls, and off we went...

Could we please just use cpu_feature_enabled()?