From mboxrd@z Thu Jan 1 00:00:00 1970 From: arnd@arndb.de (Arnd Bergmann) Date: Wed, 07 Jan 2015 09:18:50 +0100 Subject: [RFC PATCH v3 3/4] arm64:thunder: Add initial dts for Cavium's Thunder SoC in 2 Node topology. In-Reply-To: References: <1420011208-7051-1-git-send-email-ganapatrao.kulkarni@caviumnetworks.com> <3372289.4AUgcSNZN5@wuerfel> Message-ID: <2298510.9qAQRQ2lzi@wuerfel> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wednesday 07 January 2015 12:37:51 Ganapatrao Kulkarni wrote: > Hi Arnd, > > On Wed, Jan 7, 2015 at 1:32 AM, Arnd Bergmann wrote: > > On Tuesday 06 January 2015 15:04:26 Ganapatrao Kulkarni wrote: > >> On Sat, Jan 3, 2015 at 2:47 AM, Arnd Bergmann wrote: > >> > On Wednesday 31 December 2014 13:03:27 Ganapatrao Kulkarni wrote: > >> >> + cpu at 00f { > >> >> + device_type = "cpu"; > >> >> + compatible = "cavium,thunder", "arm,armv8"; > >> >> + reg = <0x0 0x00f>; > >> >> + enable-method = "psci"; > >> >> + arm,associativity = <0 0 0x00f>; > >> >> + }; > >> >> + cpu at 100 { > >> >> + device_type = "cpu"; > >> >> + compatible = "cavium,thunder", "arm,armv8"; > >> >> + reg = <0x0 0x100>; > >> >> + enable-method = "psci"; > >> >> + arm,associativity = <0 0 0x100>; > >> >> + }; > >> > > >> > What is the 0x100 offset in the last-level topology field? Does this have > >> > no significance to topology at all? I would expect that to be something > >> > like cluster number that is relevant to caching and should be represented > >> > as a separate level. > >> > >> i did not understand, can you please explain little more about " > >> should be represented as a separate level." > >> at present, i have put the hwid of a cpu. > > > > From what I undertand, the hwid of the CPU contains the "cluster" number in > > this bit position, so you typically have a shared L2 or L3 cache between > > all cores within a cluster, but separate caches in other clusters. > > > > If this is the case, there will be a measurable difference in performance > > between two processes sharing memory when running on the same cluster, > > or when running on different clusters on the same socket. If the > > performance difference is relevant, it should be described as a separate > > level in the associativity property. > you mean, the associativity as array of No, that would leave out the core number, which is required to identify the individual thread. I meant adding an extra level such as A lot of machines will leave out the number because they are built with SoCs that don't have a long-distance coherency protocol. Arnd