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Date: Tue, 10 Aug 2021 07:41:40 -0700 From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> To: "Peter Zijlstra (Intel)" <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org> Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>, Nicholas Piggin <npiggin@...il.com>, Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Len Brown <len.brown@...el.com>, Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>, Tim Chen <tim.c.chen@...ux.intel.com>, Aubrey Li <aubrey.li@...ux.intel.com>, "Ravi V. Shankar" <ravi.v.shankar@...el.com>, Ricardo Neri <ricardo.neri@...el.com>, "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>, Quentin Perret <qperret@...gle.com>, "Joel Fernandes (Google)" <joel@...lfernandes.org>, linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org, Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>, Aubrey Li <aubrey.li@...el.com>, Daniel Bristot de Oliveira <bristot@...hat.com> Subject: [PATCH v4 1/6] x86/sched: Decrease further the priorities of SMT siblings When scheduling, it is better to prefer a separate physical core rather than the SMT sibling of a high priority core. The existing formula to compute priorities takes such fact in consideration. There may exist, however, combinations of priorities (i.e., maximum frequencies) in which the priority of high-numbered SMT siblings of high-priority cores collides with the priority of low-numbered SMT siblings of low-priority cores. Consider for instance an SMT2 system with CPUs [0, 1] with priority 60 and [2, 3] with priority 30(CPUs in brackets are SMT siblings. In such a case, the resulting priorities would be [120, 60], [60, 30]. Thus, to ensure that CPU2 has higher priority than CPU1, divide the raw priority by the squared SMT iterator. The resulting priorities are [120, 30]. [60, 15]. Cc: Aubrey Li <aubrey.li@...el.com> Cc: Ben Segall <bsegall@...gle.com> Cc: Daniel Bristot de Oliveira <bristot@...hat.com> Cc: Dietmar Eggemann <dietmar.eggemann@....com> Cc: Joel Fernandes (Google) <joel@...lfernandes.org> Cc: Mel Gorman <mgorman@...e.de> Cc: Quentin Perret <qperret@...gle.com> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com> Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com> Cc: Steven Rostedt <rostedt@...dmis.org> Cc: Tim Chen <tim.c.chen@...ux.intel.com> Originally-by: Len Brown <len.brown@...el.com> Signed-off-by: Len Brown <len.brown@...el.com> Signed-off-by: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com> --- Changes since v3: * Introduced this patch Changes since v2: * N/A Changes since v1: * N/A --- arch/x86/kernel/itmt.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/itmt.c b/arch/x86/kernel/itmt.c index 1afbdd1dd777..9ff480e94511 100644 --- a/arch/x86/kernel/itmt.c +++ b/arch/x86/kernel/itmt.c @@ -198,7 +198,7 @@ void sched_set_itmt_core_prio(int prio, int core_cpu) * of the priority chain and only used when * all other high priority cpus are out of capacity. */ - smt_prio = prio * smp_num_siblings / i; + smt_prio = prio * smp_num_siblings / (i * i); per_cpu(sched_core_priority, cpu) = smt_prio; i++; } -- 2.17.1
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