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Tue, 4 Aug 2020 12:46:42 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id AB51A2B94E749; Tue, 4 Aug 2020 12:46:42 +0200 (CEST) Date: Tue, 4 Aug 2020 12:46:42 +0200 From: peterz@infradead.org To: Srikar Dronamraju Subject: Re: [PATCH 2/2] powerpc/topology: Override cpu_smt_mask Message-ID: <20200804104642.GC2657@hirez.programming.kicks-ass.net> References: <20200804033307.76111-1-srikar@linux.vnet.ibm.com> <20200804033307.76111-2-srikar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200804033307.76111-2-srikar@linux.vnet.ibm.com> X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Gautham R Shenoy , Michael Neuling , Vincent Guittot , Rik van Riel , linuxppc-dev , LKML , Ingo Molnar , Thomas Gleixner , Mel Gorman , Valentin Schneider , Dietmar Eggemann Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Aug 04, 2020 at 09:03:07AM +0530, Srikar Dronamraju wrote: > On Power9 a pair of cores can be presented by the firmware as a big-core > for backward compatibility reasons, with 4 threads per (small) core and 8 > threads per big-core. cpu_smt_mask() should generally point to the cpu mask > of the (small)core. > > In order to maintain userspace backward compatibility (with Power8 chips in > case of Power9) in enterprise Linux systems, the topology_sibling_cpumask > has to be set to big-core. Hence override the default cpu_smt_mask() to be > powerpc specific allowing for better scheduling behaviour on Power. Why does Linux userspace care about this?