linux-kernel - Re: [PATCH v7 2/3] x86/cacheinfo: Delete global num_cache

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Message-ID: <20241108115825.GAZy384e9IEr7DWvaJ@fat_crate.local>
Date: Fri, 8 Nov 2024 12:58:25 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Cc: x86@...nel.org, Andreas Herrmann <aherrmann@...e.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Chen Yu <yu.c.chen@...el.com>, Len Brown <len.brown@...el.com>,
	Radu Rendec <rrendec@...hat.com>,
	Pierre Gondois <Pierre.Gondois@....com>, Pu Wen <puwen@...on.cn>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Sudeep Holla <sudeep.holla@....com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Will Deacon <will@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	Huang Ying <ying.huang@...el.com>,
	Ricardo Neri <ricardo.neri@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/3] x86/cacheinfo: Delete global num_cache_leaves

On Tue, Oct 22, 2024 at 08:50:22PM -0700, Ricardo Neri wrote:
> I agree. Another wrapper is not needed. I did not use cache_leaves() because
> it was internal to drivers/base/cacheinfo.c I can convert it to a function
> and expose it in include/linux/cacheinfo.h. I can rename it as
> get_cacheinfo_leaves(unsigned int cpu).
> 
> Would that make sense?

I think you should use get_cpu_cacheinfo() everywhere and simply access the
struct members like ->num_leaves where you need it. No need for a bunch of
other silly one-liners.

> The only caller of init_cache_level() also checks for !cache_leaves(cpu). I
> saw no need to repeat the check here.
> 
> Also, I understand that the purpose of the function is to initialize
> cpu_cacheinfo::num_levels, which is not used on x86. Moreover,
> cpu_cacheinfo::num_levels do not depend on num_leaves.
> 
> Having said that, I see other architectures initializing both num_levels
> and num_leaves in this function.
> 
> Adding this check probably makes the x86 implementation more future-proof
> in case callers change their behavior.

But you're practically zapping its body in the next patch. So why does patch
3 even exist as a separate patch instead of being part of patch 2?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette