Commit c1e53367 authored by Srikar Dronamraju's avatar Srikar Dronamraju Committed by Michael Ellerman
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powerpc/smp: Cache CPU to chip lookup 



On systems with large CPUs per node, even with the filtered matching of
related CPUs, there can be large number of calls to cpu_to_chip_id for
the same CPU. For example with 4096 vCPU, 1 node QEMU configuration,
with 4 threads per core, system could be see upto 1024 calls to
cpu_to_chip_id() for the same CPU. On a given system, cpu_to_chip_id()
for a given CPU would always return the same. Hence cache the result in
a lookup table for use in subsequent calls.

Since all CPUs sharing the same core will belong to the same chip, the
lookup_table has an entry for one CPU per core.  chip_id_lookup_table is
not being freed and would be used on subsequent CPU online post CPU
offline.

Reported-by: default avatarDaniel Henrique Barboza <danielhb413@gmail.com>
Suggested-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Signed-off-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Tested-by: default avatarDaniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210415120934.232271-4-srikar@linux.vnet.ibm.com
parent 131c82b6

arch/powerpc/include/asm/smp.h

+1 −0
Original line number Diff line number Diff line
@@ -31,6 +31,7 @@ extern u32 *cpu_to_phys_id; 
extern bool coregroup_enabled;



extern int cpu_to_chip_id(int cpu);

extern int *chip_id_lookup_table;



#ifdef CONFIG_SMP

arch/powerpc/kernel/prom.c

+15 −4
Original line number Diff line number Diff line
@@ -65,6 +65,8 @@ 
#define DBG(fmt...)

#endif



int *chip_id_lookup_table;



#ifdef CONFIG_PPC64

int __initdata iommu_is_off;

int __initdata iommu_force_on;
@@ -914,13 +916,22 @@ EXPORT_SYMBOL(of_get_ibm_chip_id); 
int cpu_to_chip_id(int cpu)

{

	struct device_node *np;

	int ret = -1, idx;



	np = of_get_cpu_node(cpu, NULL);

	if (!np)

		return -1;

	idx = cpu / threads_per_core;

	if (chip_id_lookup_table && chip_id_lookup_table[idx] != -1)

		return chip_id_lookup_table[idx];



	np = of_get_cpu_node(cpu, NULL);

	if (np) {

		ret = of_get_ibm_chip_id(np);

		of_node_put(np);

	return of_get_ibm_chip_id(np);



		if (chip_id_lookup_table)

			chip_id_lookup_table[idx] = ret;

	}



	return ret;

}

EXPORT_SYMBOL(cpu_to_chip_id);

arch/powerpc/kernel/smp.c

+19 −2
Original line number Diff line number Diff line
@@ -1073,6 +1073,20 @@ void __init smp_prepare_cpus(unsigned int max_cpus) 
				cpu_smallcore_mask(boot_cpuid));

	}



	if (cpu_to_chip_id(boot_cpuid) != -1) {

		int idx = num_possible_cpus() / threads_per_core;



		/*

		 * All threads of a core will all belong to the same core,

		 * chip_id_lookup_table will have one entry per core.

		 * Assumption: if boot_cpuid doesn't have a chip-id, then no

		 * other CPUs, will also not have chip-id.

		 */

		chip_id_lookup_table = kcalloc(idx, sizeof(int), GFP_KERNEL);

		if (chip_id_lookup_table)

			memset(chip_id_lookup_table, -1, sizeof(int) * idx);

	}



	if (smp_ops && smp_ops->probe)

		smp_ops->probe();

}
@@ -1468,8 +1482,8 @@ static void add_cpu_to_masks(int cpu) 
{

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

	int first_thread = cpu_first_thread_sibling(cpu);

	int chip_id = cpu_to_chip_id(cpu);

	cpumask_var_t mask;

	int chip_id = -1;

	bool ret;

	int i;
@@ -1492,7 +1506,10 @@ static void add_cpu_to_masks(int cpu) 
	if (has_coregroup_support())

		update_coregroup_mask(cpu, &mask);



	if (chip_id == -1 || !ret) {

	if (chip_id_lookup_table && ret)

		chip_id = cpu_to_chip_id(cpu);



	if (chip_id == -1) {

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

		goto out;

	}