linux-kernel - Re: [RFC PATCH v2 11/35] arch_topology: Make register_cpu_capacity

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZTJqOTfDEnL9wgtY@shell.armlinux.org.uk>
Date:   Fri, 20 Oct 2023 12:53:29 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        gregkh@...uxfoundation.org
Cc:     James Morse <james.morse@....com>, linux-pm@...r.kernel.org,
        loongarch@...ts.linux.dev, linux-acpi@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, kvmarm@...ts.linux.dev,
        x86@...nel.org, Salil Mehta <salil.mehta@...wei.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        jianyong.wu@....com, justin.he@....com
Subject: Re: [RFC PATCH v2 11/35] arch_topology: Make
 register_cpu_capacity_sysctl() tolerant to late CPUs

On Thu, Sep 14, 2023 at 01:01:26PM +0100, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:37:59 +0000
> James Morse <james.morse@....com> wrote:
> 
> > register_cpu_capacity_sysctl() adds a property to sysfs that describes
> > the CPUs capacity. This is done from a subsys_initcall() that assumes
> > all possible CPUs are registered.
> > 
> > With CPU hotplug, possible CPUs aren't registered until they become
> > present, (or for arm64 enabled). This leads to messages during boot:
> > | register_cpu_capacity_sysctl: too early to get CPU1 device!
> > and once these CPUs are added to the system, the file is missing.
> > 
> > Move this to a cpuhp callback, so that the file is created once
> > CPUs are brought online. This covers CPUs that are added late by
> > mechanisms like hotplug.
> > One observable difference is the file is now missing for offline CPUs.
> > 
> > Signed-off-by: James Morse <james.morse@....com>
> > ---
> > If the offline CPUs thing is a problem for the tools that consume
> > this value, we'd need to move cpu_capacity to be part of cpu.c's
> > common_cpu_attr_groups.
> 
> I think we should do that anyway and then use an is_visible() if we want to
> change whether it is visible in offline cpus.
> 
> Dynamic sysfs file creation is horrible - particularly when done
> from an totally different file from where the rest of the attributes
> are registered.  I'm curious what the history behind that is.
> 
> Whilst here, why is there a common_cpu_attr_groups which is
> identical to the hotpluggable_cpu_attr_groups in base/cpu.c?
> 
> 
> +CC GregKH
> Given changes in drivers/base/

It would be good to have a comment on this from Greg before I post
an updated series of James' patches with most of the comments
addressed, possibly later today.

Thanks.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!