Commit 4ca234a9 authored by Srikar Dronamraju's avatar Srikar Dronamraju Committed by Michael Ellerman
Browse files

powerpc/smp: Stop updating cpu_core_mask 



Anton Blanchard reported that his 4096 vcpu KVM guest took around 30
minutes to boot. He also analyzed it to the time taken to iterate while
setting the cpu_core_mask.

Further analysis shows that cpu_core_mask and cpu_cpu_mask for any CPU
would be equal on Power. However updating cpu_core_mask took forever to
update as its a per cpu cpumask variable. Instead cpu_cpu_mask was a per
NODE /per DIE cpumask that was shared by all the respective CPUs.

Also cpu_cpu_mask is needed from a scheduler perspective. However
cpu_core_map is an exported symbol. Hence stop updating cpu_core_map
and make it point to cpu_cpu_mask.

Signed-off-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Tested-by: default avatarSatheesh Rajendran <sathnaga@linux.vnet.ibm.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200921095653.9701-3-srikar@linux.vnet.ibm.com
parent 4bce5459

arch/powerpc/include/asm/smp.h

+0 −5
Original line number Diff line number Diff line
@@ -121,11 +121,6 @@ static inline struct cpumask *cpu_sibling_mask(int cpu) 
	return per_cpu(cpu_sibling_map, cpu);

}



static inline struct cpumask *cpu_core_mask(int cpu)

{

	return per_cpu(cpu_core_map, cpu);

}



static inline struct cpumask *cpu_l2_cache_mask(int cpu)

{

	return per_cpu(cpu_l2_cache_map, cpu);

arch/powerpc/kernel/smp.c

+7 −26
Original line number Diff line number Diff line
@@ -953,12 +953,17 @@ void __init smp_prepare_cpus(unsigned int max_cpus) 
				local_memory_node(numa_cpu_lookup_table[cpu]));

		}

#endif

		/*

		 * cpu_core_map is now more updated and exists only since

		 * its been exported for long. It only will have a snapshot

		 * of cpu_cpu_mask.

		 */

		cpumask_copy(per_cpu(cpu_core_map, cpu), cpu_cpu_mask(cpu));

	}



	/* Init the cpumasks so the boot CPU is related to itself */

	cpumask_set_cpu(boot_cpuid, cpu_sibling_mask(boot_cpuid));

	cpumask_set_cpu(boot_cpuid, cpu_l2_cache_mask(boot_cpuid));

	cpumask_set_cpu(boot_cpuid, cpu_core_mask(boot_cpuid));



	if (has_coregroup_support())

		cpumask_set_cpu(boot_cpuid, cpu_coregroup_mask(boot_cpuid));
@@ -1260,9 +1265,7 @@ static void remove_cpu_from_masks(int cpu) 
{

	int i;



	/* NB: cpu_core_mask is a superset of the others */

	for_each_cpu(i, cpu_core_mask(cpu)) {

		set_cpus_unrelated(cpu, i, cpu_core_mask);

	for_each_cpu(i, cpu_cpu_mask(cpu)) {

		set_cpus_unrelated(cpu, i, cpu_l2_cache_mask);

		set_cpus_unrelated(cpu, i, cpu_sibling_mask);

		if (has_big_cores)
@@ -1312,7 +1315,6 @@ EXPORT_SYMBOL_GPL(get_physical_package_id); 
static void add_cpu_to_masks(int cpu)

{

	int first_thread = cpu_first_thread_sibling(cpu);

	int pkg_id = get_physical_package_id(cpu);

	int i;



	/*
@@ -1320,7 +1322,6 @@ static void add_cpu_to_masks(int cpu) 
	 * add it to it's own thread sibling mask.

	 */

	cpumask_set_cpu(cpu, cpu_sibling_mask(cpu));

	cpumask_set_cpu(cpu, cpu_core_mask(cpu));



	for (i = first_thread; i < first_thread + threads_per_core; i++)

		if (cpu_online(i))
@@ -1342,26 +1343,6 @@ static void add_cpu_to_masks(int cpu) 
				set_cpus_related(cpu, i, cpu_coregroup_mask);

		}

	}



	if (pkg_id == -1) {

		struct cpumask *(*mask)(int) = cpu_sibling_mask;



		/*

		 * Copy the sibling mask into core sibling mask and

		 * mark any CPUs on the same chip as this CPU.

		 */

		if (shared_caches)

			mask = cpu_l2_cache_mask;



		for_each_cpu(i, mask(cpu))

			set_cpus_related(cpu, i, cpu_core_mask);



		return;

	}



	for_each_cpu(i, cpu_online_mask)

		if (get_physical_package_id(i) == pkg_id)

			set_cpus_related(cpu, i, cpu_core_mask);

}



/* Activate a secondary processor. */

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