[PATCH 3/3] powerpc/smp: Cache CPU to chip lookup
Srikar Dronamraju
srikar at linux.vnet.ibm.com
Thu Apr 15 22:09:34 AEST 2021
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.
Suggested-by: Michael Ellerman <mpe at ellerman.id.au>
Cc: linuxppc-dev at lists.ozlabs.org
Cc: qemu-ppc at nongnu.org
Cc: Cedric Le Goater <clg at kaod.org>
Cc: David Gibson <david at gibson.dropbear.id.au>
Cc: Nathan Lynch <nathanl at linux.ibm.com>
Cc: Michael Ellerman <mpe at ellerman.id.au>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Valentin Schneider <valentin.schneider at arm.com>
Cc: Gautham R Shenoy <ego at linux.vnet.ibm.com>
Reported-by: Daniel Henrique Barboza <danielhb413 at gmail.com>
Signed-off-by: Srikar Dronamraju <srikar at linux.vnet.ibm.com>
---
arch/powerpc/include/asm/smp.h | 1 +
arch/powerpc/kernel/prom.c | 19 +++++++++++++++----
arch/powerpc/kernel/smp.c | 21 +++++++++++++++++++--
3 files changed, 35 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/include/asm/smp.h b/arch/powerpc/include/asm/smp.h
index 47081a9e13ca..03b3d010cbab 100644
--- a/arch/powerpc/include/asm/smp.h
+++ b/arch/powerpc/include/asm/smp.h
@@ -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
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 9a4797d1d40d..6d2e4a5bc471 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -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;
+
+ 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)
- return -1;
+ if (np) {
+ ret = of_get_ibm_chip_id(np);
+ of_node_put(np);
+
+ if (chip_id_lookup_table)
+ chip_id_lookup_table[idx] = ret;
+ }
- of_node_put(np);
- return of_get_ibm_chip_id(np);
+ return ret;
}
EXPORT_SYMBOL(cpu_to_chip_id);
diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index 5c7ce1d50631..50520fbea424 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c
@@ -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;
}
--
2.25.1
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