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Fri, 7 Aug 2020 07:45:21 +0000 (GMT) From: Srikar Dronamraju To: Michael Ellerman Subject: [PATCH v2 1/2] sched/topology: Allow archs to override cpu_smt_mask Date: Fri, 7 Aug 2020 13:15:16 +0530 Message-Id: <20200807074517.27957-1-srikar@linux.vnet.ibm.com> X-Mailer: git-send-email 2.26.2 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-08-07_02:2020-08-06, 2020-08-07 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 lowpriorityscore=0 clxscore=1015 malwarescore=0 mlxlogscore=999 impostorscore=0 adultscore=0 spamscore=0 priorityscore=1501 mlxscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2008070051 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 , Srikar Dronamraju , Peter Zijlstra , Mel Gorman , LKML , Valentin Schneider , linuxppc-dev , Ingo Molnar , Dietmar Eggemann Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" cpu_smt_mask tracks topology_sibling_cpumask. This would be good for most architectures. One of the users of cpu_smt_mask(), would be to identify idle-cores. On Power9, a pair of SMT4 cores can be presented by the firmware as a SMT8 core for backward compatibility reasons. Powerpc allows LPARs to be live migrated from Power8 to Power9. Do note Power8 had only SMT8 cores. Existing software which has been developed/configured for Power8 would expect to see SMT8 core. Maintaining the illusion of SMT8 core is a requirement to make that work. In order to maintain above userspace backward compatibility with previous versions of processor, Power9 onwards there is option to the firmware to advertise a pair of SMT4 cores as a fused cores aka SMT8 core. On Power9 this pair shares the L2 cache as well. However, from the scheduler's point of view, a core should be determined by SMT4, since its a completely independent unit of compute. Hence allow PowerPc architecture to override the default cpu_smt_mask() to point to the SMT4 cores in a SMT8 mode. This will ensure the scheduler is always given the right information. Cc: linuxppc-dev Cc: LKML Cc: Michael Ellerman Cc: Michael Neuling Cc: Gautham R Shenoy Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Valentin Schneider Cc: Dietmar Eggemann Cc: Mel Gorman Cc: Vincent Guittot Cc: Vaidyanathan Srinivasan Acked-by; Peter Zijlstra (Intel) Signed-off-by: Srikar Dronamraju --- Changelog v1->v2: Update the commit msg based on the discussion in community esp with Peter Zijlstra and Michael Ellerman. include/linux/topology.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/topology.h b/include/linux/topology.h index 608fa4aadf0e..ad03df1cc266 100644 --- a/include/linux/topology.h +++ b/include/linux/topology.h @@ -198,7 +198,7 @@ static inline int cpu_to_mem(int cpu) #define topology_die_cpumask(cpu) cpumask_of(cpu) #endif -#ifdef CONFIG_SCHED_SMT +#if defined(CONFIG_SCHED_SMT) && !defined(cpu_smt_mask) static inline const struct cpumask *cpu_smt_mask(int cpu) { return topology_sibling_cpumask(cpu); -- 2.18.2