From 9c9f8fb71feed144973a70455e0a4ee3da57ed2a Mon Sep 17 00:00:00 2001 From: Anju T Sudhakar Date: Mon, 10 Jun 2019 12:02:29 +0530 Subject: powerpc/perf: Use cpumask_last() to determine the designated cpu for nest/core units. Nest and core IMC (In-Memory Collection counters) assigns a particular cpu as the designated target for counter data collection. During system boot, the first online cpu in a chip gets assigned as the designated cpu for that chip(for nest-imc) and the first online cpu in a core gets assigned as the designated cpu for that core(for core-imc). If the designated cpu goes offline, the next online cpu from the same chip(for nest-imc)/core(for core-imc) is assigned as the next target, and the event context is migrated to the target cpu. Currently, cpumask_any_but() function is used to find the target cpu. Though this function is expected to return a `random` cpu, this always returns the next online cpu. If all cpus in a chip/core is offlined in a sequential manner, starting from the first cpu, the event migration has to happen for all the cpus which goes offline. Since the migration process involves a grace period, the total time taken to offline all the cpus will be significantly high. Example: In a system which has 2 sockets, with NUMA node0 CPU(s): 0-87 NUMA node8 CPU(s): 88-175 Time taken to offline cpu 88-175: real 2m56.099s user 0m0.191s sys 0m0.000s Use cpumask_last() to choose the target cpu, when the designated cpu goes online, so the migration will happen only when the last_cpu in the mask goes offline. This way the time taken to offline all cpus in a chip/core can be reduced. With the patch: Time taken to offline cpu 88-175: real 0m12.207s user 0m0.171s sys 0m0.000s Offlining all cpus in reverse order is also taken care because, cpumask_any_but() is used to find the designated cpu if the last cpu in the mask goes offline. Since cpumask_any_but() always return the first cpu in the mask, that becomes the designated cpu and migration will happen only when the first_cpu in the mask goes offline. Example: With the patch, Time taken to offline cpu from 175-88: real 0m9.330s user 0m0.110s sys 0m0.000s Signed-off-by: Anju T Sudhakar Reviewed-by: Madhavan Srinivasan Signed-off-by: Michael Ellerman --- arch/powerpc/perf/imc-pmu.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/perf/imc-pmu.c b/arch/powerpc/perf/imc-pmu.c index 3bdfc1e32096..dea243185ea4 100644 --- a/arch/powerpc/perf/imc-pmu.c +++ b/arch/powerpc/perf/imc-pmu.c @@ -362,7 +362,14 @@ static int ppc_nest_imc_cpu_offline(unsigned int cpu) */ nid = cpu_to_node(cpu); l_cpumask = cpumask_of_node(nid); - target = cpumask_any_but(l_cpumask, cpu); + target = cpumask_last(l_cpumask); + + /* + * If this(target) is the last cpu in the cpumask for this chip, + * check for any possible online cpu in the chip. + */ + if (unlikely(target == cpu)) + target = cpumask_any_but(l_cpumask, cpu); /* * Update the cpumask with the target cpu and @@ -667,7 +674,10 @@ static int ppc_core_imc_cpu_offline(unsigned int cpu) return 0; /* Find any online cpu in that core except the current "cpu" */ - ncpu = cpumask_any_but(cpu_sibling_mask(cpu), cpu); + ncpu = cpumask_last(cpu_sibling_mask(cpu)); + + if (unlikely(ncpu == cpu)) + ncpu = cpumask_any_but(cpu_sibling_mask(cpu), cpu); if (ncpu >= 0 && ncpu < nr_cpu_ids) { cpumask_set_cpu(ncpu, &core_imc_cpumask); -- cgit v1.2.3