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

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Message-ID: <20241109050550.GA15450@ranerica-svr.sc.intel.com>
Date: Fri, 8 Nov 2024 21:05:50 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
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 Fri, Nov 08, 2024 at 12:58:25PM +0100, Borislav Petkov wrote:
> 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.

Sure, I can do this.

> 
> > 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?

Because patch 2 deals with cpu_cacheinfo::num_leaves whereas patch 3 deals
with cpu_cacheinfo:::num_levels.

I think I see your point: it can be argued that both patches deal with
init_cache_level(). I can merge these two patches together.

Thanks and BR,
Ricardo