linux-kernel - Re: perf usage of arch/arm64/include/asm/cputype.h

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Message-ID: <20250616160811.GA794930@e132581.arm.com>
Date: Mon, 16 Jun 2025 17:08:11 +0100
From: Leo Yan <leo.yan@....com>
To: Yicong Yang <yangyicong@...wei.com>
Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>,
	yangyicong@...ilicon.com, James Clark <james.clark@...aro.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	Ali Saidi <alisaidi@...zon.com>, Leo Yan <leo.yan@...aro.org>,
	Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	yangjinqian <yangjinqian1@...wei.com>,
	Douglas Anderson <dianders@...omium.org>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Ian Rogers <irogers@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Kan Liang <kan.liang@...ux.intel.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: perf usage of arch/arm64/include/asm/cputype.h

On Mon, Jun 16, 2025 at 11:04:08PM +0800, Yicong Yang wrote:

[...]

> >> +static bool is_perf_midr_in_range_list(u32 midr, struct midr_range
> >> const *ranges)
> >> +{
> >> +       while (ranges->model) {
> >> +               if (midr_is_cpu_model_range(midr, ranges->model,
> >> +                                           ranges->rv_min, ranges->rv_max)) {
> >> +                       return true;
> >> +               }
> >> +               ranges++;
> >> +       }
> >> +       return false;
> >> +}
> > 
> > Maybe we can make it more general. For example, move this function into
> > a common header such as tools/perf/arch/arm64/include/cputype.h. Then,
> > util/arm-spe.c can include this header.
> > 
> 
> ok this sounds just like as before except rename the midr check function and modify the
> users in perf. will do in below steps:
> - move cpu_errata_set_target_impl()/is_midr_in_range_list() out of cputype.h
>   since they're only used in the kernel with errata information
> - introduce is_target_midr_in_range_list() in cputype.h to test certain MIDR
>   is within the ranges. (is_perf_midr_in_range_list() only make sense in
>   userspace and is a bit strange to me in a kernel header). maybe reimplement
>   is_midr_in_range_list() with is_target_midr_in_range_list() otherwise there's
>   no users in kernel
> - copy cputype.h to userspace and make users use new is_target_midr_in_range_list()
> 
> this will avoid touching the kernel too much and userspace don't need to implement
> a separate function.

My understanding is we don't need to touch anything in kernel side, we
simply add a wrapper in perf tool to call midr_is_cpu_model_range().

When introduce is_target_midr_in_range_list() in kernel's cputype.h,
if no consumers in kernel use it and only useful for perf tool, then
it is unlikely to be accepted.

Thanks,
Leo