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![Andrii Nakryiko](/assets/img/avatar_default.png)
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>
198 lines
4.8 KiB
C
198 lines
4.8 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/objpool.h>
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#include <linux/slab.h>
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#include <linux/vmalloc.h>
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#include <linux/atomic.h>
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#include <linux/irqflags.h>
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#include <linux/cpumask.h>
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#include <linux/log2.h>
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/*
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* objpool: ring-array based lockless MPMC/FIFO queues
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*
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* Copyright: wuqiang.matt@bytedance.com,mhiramat@kernel.org
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*/
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/* initialize percpu objpool_slot */
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static int
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objpool_init_percpu_slot(struct objpool_head *pool,
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struct objpool_slot *slot,
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int nodes, void *context,
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objpool_init_obj_cb objinit)
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{
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void *obj = (void *)&slot->entries[pool->capacity];
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int i;
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/* initialize elements of percpu objpool_slot */
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slot->mask = pool->capacity - 1;
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for (i = 0; i < nodes; i++) {
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if (objinit) {
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int rc = objinit(obj, context);
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if (rc)
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return rc;
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}
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slot->entries[slot->tail & slot->mask] = obj;
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obj = obj + pool->obj_size;
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slot->tail++;
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slot->last = slot->tail;
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pool->nr_objs++;
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}
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return 0;
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}
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/* allocate and initialize percpu slots */
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static int
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objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
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void *context, objpool_init_obj_cb objinit)
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{
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int i, cpu_count = 0;
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for (i = 0; i < nr_cpu_ids; i++) {
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struct objpool_slot *slot;
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int nodes, size, rc;
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/* skip the cpu node which could never be present */
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if (!cpu_possible(i))
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continue;
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/* compute how many objects to be allocated with this slot */
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nodes = nr_objs / pool->nr_possible_cpus;
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if (cpu_count < (nr_objs % pool->nr_possible_cpus))
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nodes++;
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cpu_count++;
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size = struct_size(slot, entries, pool->capacity) +
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pool->obj_size * nodes;
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/*
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* here we allocate percpu-slot & objs together in a single
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* allocation to make it more compact, taking advantage of
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* warm caches and TLB hits. in default vmalloc is used to
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* reduce the pressure of kernel slab system. as we know,
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* mimimal size of vmalloc is one page since vmalloc would
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* always align the requested size to page size
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*/
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if (pool->gfp & GFP_ATOMIC)
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slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
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else
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slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
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cpu_to_node(i), __builtin_return_address(0));
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if (!slot)
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return -ENOMEM;
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memset(slot, 0, size);
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pool->cpu_slots[i] = slot;
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/* initialize the objpool_slot of cpu node i */
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rc = objpool_init_percpu_slot(pool, slot, nodes, context, objinit);
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if (rc)
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return rc;
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}
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return 0;
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}
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/* cleanup all percpu slots of the object pool */
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static void objpool_fini_percpu_slots(struct objpool_head *pool)
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{
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int i;
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if (!pool->cpu_slots)
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return;
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for (i = 0; i < nr_cpu_ids; i++)
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kvfree(pool->cpu_slots[i]);
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kfree(pool->cpu_slots);
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}
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/* initialize object pool and pre-allocate objects */
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int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
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gfp_t gfp, void *context, objpool_init_obj_cb objinit,
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objpool_fini_cb release)
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{
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int rc, capacity, slot_size;
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/* check input parameters */
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if (nr_objs <= 0 || nr_objs > OBJPOOL_NR_OBJECT_MAX ||
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object_size <= 0 || object_size > OBJPOOL_OBJECT_SIZE_MAX)
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return -EINVAL;
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/* align up to unsigned long size */
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object_size = ALIGN(object_size, sizeof(long));
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/* calculate capacity of percpu objpool_slot */
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capacity = roundup_pow_of_two(nr_objs);
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if (!capacity)
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return -EINVAL;
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/* initialize objpool pool */
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memset(pool, 0, sizeof(struct objpool_head));
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pool->nr_possible_cpus = num_possible_cpus();
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pool->obj_size = object_size;
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pool->capacity = capacity;
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pool->gfp = gfp & ~__GFP_ZERO;
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pool->context = context;
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pool->release = release;
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slot_size = nr_cpu_ids * sizeof(struct objpool_slot);
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pool->cpu_slots = kzalloc(slot_size, pool->gfp);
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if (!pool->cpu_slots)
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return -ENOMEM;
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/* initialize per-cpu slots */
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rc = objpool_init_percpu_slots(pool, nr_objs, context, objinit);
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if (rc)
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objpool_fini_percpu_slots(pool);
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else
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refcount_set(&pool->ref, pool->nr_objs + 1);
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return rc;
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}
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EXPORT_SYMBOL_GPL(objpool_init);
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/* release whole objpool forcely */
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void objpool_free(struct objpool_head *pool)
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{
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if (!pool->cpu_slots)
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return;
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/* release percpu slots */
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objpool_fini_percpu_slots(pool);
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/* call user's cleanup callback if provided */
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if (pool->release)
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pool->release(pool, pool->context);
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}
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EXPORT_SYMBOL_GPL(objpool_free);
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/* drop the allocated object, rather reclaim it to objpool */
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int objpool_drop(void *obj, struct objpool_head *pool)
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{
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if (!obj || !pool)
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return -EINVAL;
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if (refcount_dec_and_test(&pool->ref)) {
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objpool_free(pool);
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return 0;
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}
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return -EAGAIN;
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}
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EXPORT_SYMBOL_GPL(objpool_drop);
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/* drop unused objects and defref objpool for releasing */
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void objpool_fini(struct objpool_head *pool)
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{
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int count = 1; /* extra ref for objpool itself */
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/* drop all remained objects from objpool */
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while (objpool_pop(pool))
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count++;
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if (refcount_sub_and_test(count, &pool->ref))
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objpool_free(pool);
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}
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EXPORT_SYMBOL_GPL(objpool_fini);
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