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Date: Wed, 14 Jan 2015 11:41:17 -0500 From: Don Dutile <ddutile@...hat.com> To: Arnd Bergmann <arnd@...db.de>, linux-arm-kernel@...ts.infradead.org CC: Jon Masters <jcm@...hat.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: sysfs topology for arm64 cluster_id On 01/14/2015 06:24 AM, Arnd Bergmann wrote: > On Tuesday 13 January 2015 19:47:00 Jon Masters wrote: >> Hi Folks, >> >> TLDR: I would like to consider the value of adding something like >> "cluster_siblings" or similar in sysfs to describe ARM topology. >> >> A quick question on intended data representation in /sysfs topology >> before I ask the team on this end to go down the (wrong?) path. On ARM >> systems today, we have a hierarchical CPU topology: >> >> Socket ---- Coherent Interonnect ---- Socket >> | | >> Cluster0 ... ClusterN Cluster0 ... ClusterN >> | | | | >> Core0...CoreN Core0...CoreN Core0...CoreN Core0...CoreN >> | | | | | | | | >> T0..TN T0..Tn T0..TN T0..TN T0..TN T0..TN T0..TN T0..TN >> >> Where we might (or might not) have threads in individual cores (a la SMT >> - it's allowed in the architecture at any rate) and we group cores >> together into units of clusters usually 2-4 cores in size (though this >> varies between implementations, some of which have different but similar >> concepts, such as AppliedMicro Potenza PMDs CPU complexes of dual >> cores). There are multiple clusters per "socket", and there might be an >> arbitrary number of sockets. We'll start to enable NUMA soon. > > Have you taken a look at the NUMA patches that Ganapatrao Kulkarni > has sent out? These encode the system-wide topology based on the model > from IBM Power machines. > Thanks for that ptr! I'll take a look at this code today. >> Is it not a good idea to expose the cluster details directly in sysfs >> and have these utilities understand the possible extra level in the >> calculation? Or do we want to just fudge the numbers (as seems to be the >> case in some systems I am seeing) to make the x86 model add up? >> >> Let me know the preferred course... > > I like the idea of encoding the topology independent of the specific > levels implemented in hardware, and we could use that same model > that we have in DT to represent things to user space, or that > can directly access the "arm,associativity" properties in > /sys/firmware/devicetree/base, but that would not be portable to > ACPI based systems. > > In the platform that Ganapatrao is interested in, there are no clusters, > but they have two levels of NUMA topology (sockets and boards), and > I could well imagine systems that have more than those two, or systems > that have multiple levels below a socket (e.g. chip, cluster, core, > thread) that all share the same NUMA node because they have a common > memory controller. > > It would be nice to find a good representation for sysfs that covers > all of these cases, and that also shows the associativity of I/O > devices. > Caches too (and cpu associativity to them, esp. L2) > Arnd > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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