linux-kernel - Re: [PATCH 01/32] perf: Allow a PMU to have a parent

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Message-ID: <ZH8vUKt+iCF4M70d@FVFF77S0Q05N.cambridge.arm.com>
Date:   Tue, 6 Jun 2023 14:06:24 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Yicong Yang <yangyicong@...wei.com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Will Deacon <will@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, gregkh@...uxfoundation.org,
        yangyicong@...ilicon.com, linuxarm@...wei.com,
        Dan Williams <dan.j.williams@...el.com>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Jiucheng Xu <jiucheng.xu@...ogic.com>,
        Khuong Dinh <khuong@...amperecomputing.com>,
        Robert Richter <rric@...nel.org>,
        Atish Patra <atishp@...shpatra.org>,
        Anup Patel <anup@...infault.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Frank Li <Frank.li@....com>,
        Shuai Xue <xueshuai@...ux.alibaba.com>,
        Vineet Gupta <vgupta@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Dave Jiang <dave.jiang@...el.com>, Wu Hao <hao.wu@...el.com>,
        Tom Rix <trix@...hat.com>, linux-fpga@...r.kernel.org,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Liang Kan <kan.liang@...ux.intel.com>
Subject: Re: [PATCH 01/32] perf: Allow a PMU to have a parent

On Thu, Apr 06, 2023 at 09:49:38PM +0200, Peter Zijlstra wrote:
> On Thu, Apr 06, 2023 at 05:44:45PM +0100, Jonathan Cameron wrote:
> > On Thu, 6 Apr 2023 14:40:40 +0200
> > Peter Zijlstra <peterz@...radead.org> wrote:
> > 
> > > On Thu, Apr 06, 2023 at 11:16:07AM +0100, Jonathan Cameron wrote:
> > > 
> > > > In the long run I agree it would be good.  Short term there are more instances of
> > > > struct pmu that don't have parents than those that do (even after this series).
> > > > We need to figure out what to do about those before adding checks on it being
> > > > set.  
> > > 
> > > Right, I don't think you've touched *any* of the x86 PMUs for example,
> > > and getting everybody that boots an x86 kernel a warning isn't going to
> > > go over well :-)
> > > 
> > 
> > It was tempting :) "Warning: Parentless PMU: try a different architecture."
> 
> Haha!
> 
> > I'd love some inputs on what the x86 PMU devices parents should be?
> > CPU counters in general tend to just spin out of deep in the architecture code.
> 
> For the 'simple' ones I suppose we can use the CPU device.

Uh, *which* CPU device? Do we have a container device for all CPUs?

> > My overall favorite is an l2 cache related PMU that is spun up in
> > arch/arm/kernel/irq.c init_IRQ()

That's an artifact of the L2 cache controller driver getting initialized there;
ideally we'd have a device for the L2 cache itself (which presumably should
hang off an aggregate CPU device).

> Yeah, we're going to have a ton of them as well. Some of them are PCI
> devices and have a clear parent, others, not so much :/

In a number of places the only thing we have is the PMU driver, and we don't
have a driver (or device) for the HW block it's a part of. Largely that's
interconnect PMUs; we could create container devices there.

Mark.