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From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc: x86@kernel.org, Borislav Petkov <bp@suse.de>,
	Ingo Molnar <mingo@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Tony Luck <tony.luck@intel.com>, Len Brown <len.brown@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	"Gautham R. Shenoy" <ego@linux.vnet.ibm.com>,
	Kan Liang <kan.liang@linux.intel.com>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Subject: Re: [PATCH 1/4] drivers core: Introduce CPU type sysfs interface
Date: Wed, 7 Oct 2020 07:15:46 +0200	[thread overview]
Message-ID: <20201007051546.GA47583@kroah.com> (raw)
In-Reply-To: <20201007031447.GB27938@ranerica-svr.sc.intel.com>

On Tue, Oct 06, 2020 at 08:14:47PM -0700, Ricardo Neri wrote:
> On Tue, Oct 06, 2020 at 09:37:44AM +0200, Greg Kroah-Hartman wrote:
> > On Mon, Oct 05, 2020 at 05:57:36PM -0700, Ricardo Neri wrote:
> > > On Sat, Oct 03, 2020 at 10:53:45AM +0200, Greg Kroah-Hartman wrote:
> > > > On Fri, Oct 02, 2020 at 06:17:42PM -0700, Ricardo Neri wrote:
> > > > > Hybrid CPU topologies combine CPUs of different microarchitectures in the
> > > > > same die. Thus, even though the instruction set is compatible among all
> > > > > CPUs, there may still be differences in features (e.g., some CPUs may
> > > > > have counters that others CPU do not). There may be applications
> > > > > interested in knowing the type of micro-architecture topology of the
> > > > > system to make decisions about process affinity.
> > > > > 
> > > > > While the existing sysfs for capacity (/sys/devices/system/cpu/cpuX/
> > > > > cpu_capacity) may be used to infer the types of micro-architecture of the
> > > > > CPUs in the platform, it may not be entirely accurate. For instance, two
> > > > > subsets of CPUs with different types of micro-architecture may have the
> > > > > same capacity due to power or thermal constraints.
> > > > > 
> > > > > Create the new directory /sys/devices/system/cpu/types. Under such
> > > > > directory, create individual subdirectories for each type of CPU micro-
> > > > > architecture. Each subdirectory will have cpulist and cpumap files. This
> > > > > makes it convenient for user space to read all the CPUs of the same type
> > > > > at once without having to inspect each CPU individually.
> > > > > 
> > > > > Implement a generic interface using weak functions that architectures can
> > > > > override to indicate a) support for CPU types, b) the CPU type number, and
> > > > > c) a string to identify the CPU vendor and type.
> > > > > 
> > > > > For example, an x86 system with one Intel Core and four Intel Atom CPUs
> > > > > would look like this (other architectures have the hooks to use whatever
> > > > > directory naming convention below "types" that meets their needs):
> > > > > 
> > > > > user@host:~$: ls /sys/devices/system/cpu/types
> > > > > intel_atom_0  intel_core_0
> > > > > 
> > > > > user@host:~$ ls /sys/devices/system/cpu/types/intel_atom_0
> > > > > cpulist cpumap
> > > > > 
> > > > > user@host:~$ ls /sys/devices/system/cpu/types/intel_core_0
> > > > > cpulist cpumap
> > > > > 
> > > > > user@host:~$ cat /sys/devices/system/cpu/types/intel_atom_0/cpumap
> > > > > 0f
> > > > > 
> > > > > user@host:~$ cat /sys/devices/system/cpu/types/intel_atom_0/cpulist
> > > > > 0-3
> > > > > 
> > > > > user@ihost:~$ cat /sys/devices/system/cpu/types/intel_core_0/cpumap
> > > > > 10
> > > > > 
> > > > > user@host:~$ cat /sys/devices/system/cpu/types/intel_core_0/cpulist
> > > > > 4
> > > 
> > > Thank you for the quick and detailed Greg!
> > > 
> > > > 
> > > > The output of 'tree' sometimes makes it easier to see here, or:
> > > > 	grep -R . *
> > > > also works well.
> > > 
> > > Indeed, this would definitely make it more readable.
> > > 
> > > > 
> > > > > On non-hybrid systems, the /sys/devices/system/cpu/types directory is not
> > > > > created. Add a hook for this purpose.
> > > > 
> > > > Why should these not show up if the system is not "hybrid"?
> > > 
> > > My thinking was that on a non-hybrid system, it does not make sense to
> > > create this interface, as all the CPUs will be of the same type.
> > 
> > Why not just have this an attribute type in the existing cpuX directory?
> > Why do this have to be a totally separate directory and userspace has to
> > figure out to look in two different spots for the same cpu to determine
> > what it is?
> 
> But if the type is located under cpuX, usespace would need to traverse
> all the CPUs and create its own cpu masks. Under the types directory it
> would only need to look once for each type of CPU, IMHO.

What does a "mask" do?  What does userspace care about this?  You would
have to create it by traversing the directories you are creating anyway,
so it's not much different, right?

> > That feels wasteful, it should be much simpler to use the existing
> > object, right?
> > 
> > That way, you also show the "type" of all cpus, no matter if they are
> > "hybrid" or not, again, making userspace deal with things in a much
> > simpler manner.
> 
> Indeed, that would be simpler to implement, and perhaps a natural extension
> of the existing interface. 
> 
> Lastly, legacy and non-hybrid parts will not have a type defined. Thus,
> it may not make sense for them to expose a type in sysfs.

That's fine, not having a sysfs file if you don't know the type is fine.
Or you can fix that up and show the type of those as well, why wouldn't
you want to?

> > > I thought of this as maybe intel_atcm vs a potential amd_minizen. I
> > > guess arch is sufficient, as there will never be an amd_atom.
> > 
> > Even if there is, that can be part of the cpu "type" that you have for
> > your enumerated type, right?
> 
> Indeed. The interface I propose lets archs define their own string
> names.

Arches _should_ define their own names, otherwise who would?

thanks,

greg k-h

  reply	other threads:[~2020-10-07  5:15 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-03  1:17 [PATCH 0/4] drivers core: Introduce CPU type sysfs interface Ricardo Neri
2020-10-03  1:17 ` [PATCH 1/4] " Ricardo Neri
2020-10-03  3:27   ` Randy Dunlap
2020-10-06  1:15     ` Ricardo Neri
2020-10-10  3:14       ` Randy Dunlap
2020-10-03  8:53   ` Greg Kroah-Hartman
2020-10-03 11:05     ` Greg Kroah-Hartman
2020-10-06  1:08       ` Ricardo Neri
2020-10-06  0:57     ` Ricardo Neri
2020-10-06  7:37       ` Greg Kroah-Hartman
2020-10-07  3:14         ` Ricardo Neri
2020-10-07  5:15           ` Greg Kroah-Hartman [this message]
2020-10-08  3:34             ` Ricardo Neri
2020-11-12  6:19             ` Brice Goglin
2020-11-12  6:42               ` Greg Kroah-Hartman
2020-11-12  9:10                 ` Brice Goglin
2020-11-12 10:49                   ` Greg Kroah-Hartman
2020-11-17 15:55                     ` Brice Goglin
2020-11-18 10:45                       ` Brice Goglin
2020-11-18 10:57                         ` Greg Kroah-Hartman
     [not found]                     ` <38f290d2-4c3a-d1b0-f3cc-a0897ea10abd@gmail.com>
2020-11-12 11:34                       ` Greg Kroah-Hartman
2020-11-19  8:25                       ` Fox Chen
2020-10-03  1:17 ` [PATCH 2/4] x86/cpu: Describe hybrid CPUs in cpuinfo_x86 Ricardo Neri
2020-10-03  4:07   ` kernel test robot
2020-10-03  1:17 ` [PATCH 3/4] x86/cpu/intel: Add function to get name of hybrid CPU types Ricardo Neri
2020-10-03  1:17 ` [PATCH 4/4] x86/cpu/topology: Implement the CPU type sysfs interface Ricardo Neri
2020-10-03  3:33   ` Randy Dunlap
2020-10-03  5:28   ` kernel test robot
2020-10-03  8:55   ` Greg Kroah-Hartman
2020-10-06  1:05     ` Ricardo Neri
2020-10-03  8:49 ` [PATCH 0/4] drivers core: Introduce " Borislav Petkov
2020-10-06  0:27   ` Ricardo Neri
2020-10-06  8:51 ` Qais Yousef
2020-10-07  2:50   ` Ricardo Neri

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