Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Thu, 6 Apr 2023 19:08:45 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Yicong Yang <yangyicong@huawei.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Will Deacon <will@kernel.org>, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, yangyicong@hisilicon.com,
        linuxarm@huawei.com, Dan Williams <dan.j.williams@intel.com>,
        Shaokun Zhang <zhangshaokun@hisilicon.com>,
        Jiucheng Xu <jiucheng.xu@amlogic.com>,
        Khuong Dinh <khuong@os.amperecomputing.com>,
        Robert Richter <rric@kernel.org>,
        Atish Patra <atishp@atishpatra.org>,
        Anup Patel <anup@brainfault.org>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <andersson@kernel.org>,
        Frank Li <Frank.li@nxp.com>,
        Shuai Xue <xueshuai@linux.alibaba.com>,
        Vineet Gupta <vgupta@kernel.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Dave Jiang <dave.jiang@intel.com>, Wu Hao <hao.wu@intel.com>,
        Tom Rix <trix@redhat.com>, linux-fpga@vger.kernel.org,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Liang Kan <kan.liang@linux.intel.com>
Subject: Re: [PATCH 01/32] perf: Allow a PMU to have a parent
Message-ID: <2023040610-morbidly-supermom-e81c@gregkh>
References: <20230404134225.13408-1-Jonathan.Cameron@huawei.com>
 <20230404134225.13408-2-Jonathan.Cameron@huawei.com>
 <61f8e489-ae76-38d6-2da0-43cf3c17853d@huawei.com>
 <20230406111607.00007be5@Huawei.com>
 <20230406124040.GD392176@hirez.programming.kicks-ass.net>
 <20230406174445.0000235c@Huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230406174445.0000235c@Huawei.com>
Precedence: bulk

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@infradead.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."
> 
> 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.
> 
> My overall favorite is an l2 cache related PMU that is spun up in
> arch/arm/kernel/irq.c init_IRQ()
> 
> I'm just not going to try and figure out why...

Why not change the api to force a parent to be passed in?  And if one
isn't, we make it a "virtual" device and throw it in the class for them?

thanks,

greg k-h