linux-kernel - Re: [PATCH 4/4] driver core: Allow showing cpu as offline if not valid in cpuset context

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Date:   Mon, 14 Jun 2021 19:00:53 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Waiman Long <llong@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Iurii Zaikin <yzaikin@...gle.com>, x86@...nel.org,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 4/4] driver core: Allow showing cpu as offline if not
 valid in cpuset context

On Mon, Jun 14, 2021 at 12:32:01PM -0400, Waiman Long wrote:
> On 6/14/21 11:52 AM, Greg KH wrote:
> > On Mon, Jun 14, 2021 at 11:23:06AM -0400, Waiman Long wrote:
> > > Make /sys/devices/system/cpu/cpu<n>/online file to show a cpu as
> > > offline if it is not a valid cpu in a proper cpuset context when the
> > > cpuset_bound_cpuinfo sysctl parameter is turned on.
> > This says _what_ you are doing, but I do not understand _why_ you want
> > to do this.
> > 
> > What is going to use this information?  And now you are showing more
> > files than you previously did, so what userspace tool is now going to
> > break?
> 
> One reason that is provided by the customer asking for this functionality is
> because some applications use the number of cpu cores for licensing purpose.
> Even though the applications are running in a container with a smaller set
> of cpus, they may still charge as if all the cpus are available. They ended
> up using a bind mount to mount over the cpuX/online file.

Great, then stick with the bind mount for foolish things like that.

There's no technical reason for doing this then, just marketing?

thanks,

greg k-h