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objpool: cache nr_possible_cpus() and avoid caching nr_cpu_ids

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Profiling shows that calling nr_possible_cpus() in objpool_pop() takes
a noticeable amount of CPU (when profiled on 80-core machine), as we
need to recalculate number of set bits in a CPU bit mask. This number
can't change, so there is no point in paying the price for recalculating
it. As such, cache this value in struct objpool_head and use it in
objpool_pop().

On the other hand, cached pool->nr_cpus isn't necessary, as it's not
used in hot path and is also a pretty trivial value to retrieve. So drop
pool->nr_cpus in favor of using nr_cpu_ids everywhere. This way the size
of struct objpool_head remains the same, which is a nice bonus.

Same BPF selftests benchmarks were used to evaluate the effect. Using
changes in previous patch (inlining of objpool_pop/objpool_push) as
baseline, here are the differences:

BASELINE
========
kretprobe      :    9.937 ± 0.174M/s
kretprobe-multi:   10.440 ± 0.108M/s

AFTER
=====
kretprobe      :   10.106 ± 0.120M/s (+1.7%)
kretprobe-multi:   10.515 ± 0.180M/s (+0.7%)

Link: https://lore.kernel.org/all/20240424215214.3956041-3-andrii@kernel.org/

Cc: Matt (Qiang) Wu <wuqiang.matt@bytedance.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
This commit is contained in:
Andrii Nakryiko 2024-04-24 14:52:14 -07:00 committed by Masami Hiramatsu (Google)
parent a3b00f10da
commit 78d0b16127
2 changed files with 9 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/objpool.h
View File

@ -73,7 +73,7 @@ typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
* struct objpool_head - object pooling metadata
* @obj_size: object size, aligned to sizeof(void *)
* @nr_objs: total objs (to be pre-allocated with objpool)
* @nr_cpus: local copy of nr_cpu_ids
* @nr_possible_cpus: cached value of num_possible_cpus()
* @capacity: max objs can be managed by one objpool_slot
* @gfp: gfp flags for kmalloc & vmalloc
* @ref: refcount of objpool
@ -85,7 +85,7 @@ typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
struct objpool_head {
int obj_size;
int nr_objs;
int nr_cpus;
int nr_possible_cpus;
int capacity;
gfp_t gfp;
refcount_t ref;
@ -176,7 +176,7 @@ static inline void *objpool_pop(struct objpool_head *pool)
raw_local_irq_save(flags);
cpu = raw_smp_processor_id();
for (i = 0; i < num_possible_cpus(); i++) {
for (i = 0; i < pool->nr_possible_cpus; i++) {
obj = __objpool_try_get_slot(pool, cpu);
if (obj)
break;

12
lib/objpool.c
View File

@ -50,7 +50,7 @@ objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
{
int i, cpu_count = 0;
for (i = 0; i < pool->nr_cpus; i++) {
for (i = 0; i < nr_cpu_ids; i++) {
struct objpool_slot *slot;
int nodes, size, rc;
@ -60,8 +60,8 @@ objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
continue;
/* compute how many objects to be allocated with this slot */
nodes = nr_objs / num_possible_cpus();
if (cpu_count < (nr_objs % num_possible_cpus()))
nodes = nr_objs / pool->nr_possible_cpus;
if (cpu_count < (nr_objs % pool->nr_possible_cpus))
nodes++;
cpu_count++;
@ -103,7 +103,7 @@ static void objpool_fini_percpu_slots(struct objpool_head *pool)
if (!pool->cpu_slots)
return;
for (i = 0; i < pool->nr_cpus; i++)
for (i = 0; i < nr_cpu_ids; i++)
kvfree(pool->cpu_slots[i]);
kfree(pool->cpu_slots);
}
@ -130,13 +130,13 @@ int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
/* initialize objpool pool */
memset(pool, 0, sizeof(struct objpool_head));
pool->nr_cpus = nr_cpu_ids;
pool->nr_possible_cpus = num_possible_cpus();
pool->obj_size = object_size;
pool->capacity = capacity;
pool->gfp = gfp & ~__GFP_ZERO;
pool->context = context;
pool->release = release;
slot_size = pool->nr_cpus * sizeof(struct objpool_slot);
slot_size = nr_cpu_ids * sizeof(struct objpool_slot);
pool->cpu_slots = kzalloc(slot_size, pool->gfp);
if (!pool->cpu_slots)
return -ENOMEM;