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larytet/lockfree_hashtable.c

Last active September 13, 2023 14:58
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A simple hashtable for Linux kernel drivers
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lockfree_hashtable.c
/**
* Lockfree is a set of lockfree containers for Linux and Linux kernel
* Copyright (C) <2017> Arkady Miasnikov
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/**
* Implementation of lockfree linear probing hashtable
* The hashtable targets SystemTap environment where a typical key is thread ID
* The number of probes is limited by a constant. The index is not wrapping around,
* but instead the hashtable allocates enough memory to handle linear probing in the end
* of the table
*
* Limitation: a specific entry (a specific key) can be inserted and deleted by one thread.
*
* Performance: a core can make above 13M add&remove operations per second, cost of a
* single operation is under 20nano which is an equivalent of 50-100 opcodes.
*/
#pragma once
#ifdef __KERNEL__
# include "linux/vmalloc.h"
# include "linux/printk.h"
# define DEV_NAME "lockless"
# define PRINTF(s, ...) printk(KERN_ALERT DEV_NAME ": %s: " s "\n", __func__, __VA_ARGS__)
# define PRIu64 "llu"
#else
# include <stdlib.h>
# include <stdio.h>
# include <inttypes.h>
# define PRINTF(s, ...) printf("%s: " s "\n", __func__, __VA_ARGS__)
# define likely(x) __builtin_expect(!!(x), 1) // !!(x) will return 1 for any x != 0
# define unlikely(x) __builtin_expect(!!(x), 0)
# define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
#endif
#define __sync_access(x) (*(volatile __typeof__(*x) *) (x))
/**
* Based on https://gist.github.com/badboy/6267743
* http://burtleburtle.net/bob/hash/integer.html
* I replace the 'long key' by 'unsigned key' and unsigned Java right shifts
* by regular C/C++ right shifts
* I adopt the hash function for 22 (PID_MAX_LIMIT) bits integers
*/
static uint32_t hash32shift(uint32_t key)
{
key = ~key + (key << 10); // key = (key << 15) - key - 1;
key = key ^ (key >> 7);
key = key + (key << 1);
key = key ^ (key >> 2);
key = key * 187; // key = (key + (key << 3)) + (key << 11);
key = key ^ (key >> 11);
return key;
}
static uint32_t hash_none(uint32_t key)
{
return key;
}
typedef struct
{
uint64_t insert;
uint64_t remove;
uint64_t search;
uint64_t collision;
uint64_t insert_err;
uint64_t remove_err;
} hashtable_stat_t;
typedef struct
{
const char *name;
size_t bits;
uint32_t (*hashfunction)(uint32_t);
size_t __size;
size_t __memory_size;
hashtable_stat_t __stat;
void *__table;
} hashtable_t;
static hashtable_t *hashtable_registry[64];
static int hashtable_show(char *buf, size_t len)
{
size_t i;
int rc;
size_t chars = 0;
rc = snprintf(buf+chars, len-chars, "\n%-25s %12s %12s %12s %12s %12s %12s %12s %12s %12s \n",
"Name", "Size", "Memory", "Ops", "Insert", "Remove", "Search", "Collision", "InsertErr", "RemoveErr");
chars += rc;
for (i = 0;i < ARRAY_SIZE(hashtable_registry);i++)
{
hashtable_t *hashtable = hashtable_registry[i];
hashtable_stat_t *stat;
if (!hashtable)
continue;
stat = &hashtable->__stat;
rc = snprintf(buf+chars, len-chars, "%-25s %12zu %12zu %12" PRIu64 " %12" PRIu64 " %12" PRIu64 " %12" PRIu64 " %12" PRIu64 " %12" PRIu64 " %12" PRIu64 "\n",
hashtable->name, hashtable->__size, hashtable->__memory_size,
stat->insert+stat->remove+stat->search, stat->insert, stat->remove, stat->search, stat->collision, stat->insert_err, stat->remove_err
);
chars += rc;
}
return chars;
}
static void hashtable_registry_add(hashtable_t *table)
{
size_t i;
for (i = 0;i < ARRAY_SIZE(hashtable_registry);i++)
{
hashtable_t *registry = hashtable_registry[i];
if (registry == table)
{
PRINTF("Hashtable %s already registered", table->name);
break;
}
if (!registry)
{
PRINTF("Register hashtable %s", table->name);
hashtable_registry[i] = table;
break;
}
}
}
static void hashtable_registry_remove(hashtable_t *table)
{
size_t i;
for (i = 0;i < ARRAY_SIZE(hashtable_registry);i++)
{
hashtable_t *registry = hashtable_registry[i];
if (registry == table)
{
PRINTF("Remove hashtable %s from the registry", table->name);
hashtable_registry[i] = NULL;
}
}
}
static inline size_t hashtable_get_index(const hashtable_t *hashtable, const uint32_t hash) \
{ \
return hash & (hashtable->__size - 1); \
} \
static void *hashtable_alloc(size_t size)
{
#ifdef __KERNEL__
void *p;
size = PAGE_ALIGN(size);
p = vmalloc(size);
if (p)
{
unsigned long long adr = (unsigned long long) p;
while (size > 0)
{
SetPageReserved(vmalloc_to_page((void *)adr));
adr += PAGE_SIZE;
size -= PAGE_SIZE;
}
}
return p;
#else
return malloc(size);
#endif
}
static void hashtable_free(void *p, size_t size)
{
#ifdef __KERNEL__
if (p)
{
unsigned long long adr = (unsigned long long) p;
while ((long) size > 0) {
ClearPageReserved(vmalloc_to_page((void *)adr));
adr += PAGE_SIZE;
size -= PAGE_SIZE;
}
vfree(p);
}
#else
free(p);
#endif
}
static void hashtable_close(hashtable_t *hashtable)
{
if (hashtable->__table)
{
hashtable_free(hashtable->__table, hashtable->__memory_size);
}
else
{
PRINTF("Failed to free null pointer for the hashtable %s", hashtable->name);
}
hashtable_registry_remove(hashtable);
}
#ifdef __KERNEL__
# define HASHTABLE_CMPXCHG(key, val, new_val) cmpxchg(key, val, new_val)
#else
# define HASHTABLE_CMPXCHG(key, val, new_val) __sync_val_compare_and_swap(key, val, new_val)
#endif
#if 1
#ifdef __KERNEL__
# define HASHTABLE_BARRIER() barrier()
#else
# define HASHTABLE_BARRIER() __sync_synchronize()
#endif
#else
# define HASHTABLE_BARRIER()
#endif
#define HASHTABLE_SLOT_ADDR(hashtable, tokn, index) &(((hashtable_## tokn ##_slot_t*)hashtable->__table)[index])
/**
* Illegal TID can be (PID_MAX_LIMIT+1)
* Illegal data is 0 for TID, -1 for FD, etc (this is optional)
*/
#define DECLARE_HASHTABLE(tokn, data_type, max_tries, illegal_key, illegal_data) \
\
typedef struct \
{ \
volatile uint32_t key; \
data_type data; \
} hashtable_## tokn ## _slot_t; \
\
static void hashtable_## tokn ## _init_slot(hashtable_## tokn ## _slot_t *slot) \
{ \
slot->key = illegal_key; \
slot->data = illegal_data; \
} \
\
/** \
* Calculate number of slots in the hash table \
* I add max_tries on top to ensure that there are max_tries slots after the \
* end of the table \
*/ \
static size_t hashtable_## tokn ##_memory_size(const int bits) \
{ \
size_t slots = (1 << bits) + max_tries; \
return (sizeof(hashtable_## tokn ## _slot_t) * slots); \
} \
\
static int hashtable_## tokn ##_init(hashtable_t *hashtable) \
{ \
size_t memory_size = hashtable_## tokn ## _memory_size(hashtable->bits); \
void *p = hashtable_alloc(memory_size); \
size_t i; \
if (p) \
{ \
if (hashtable->hashfunction == NULL) \
{ \
hashtable->hashfunction = hash32shift; \
} \
hashtable->__size = (1 << hashtable->bits); \
hashtable->__memory_size = memory_size; \
hashtable->__table = p; \
for (i = 0;i < hashtable->__size;i++) \
{ \
hashtable_## tokn ## _init_slot(HASHTABLE_SLOT_ADDR(hashtable, tokn, i)); \
} \
hashtable_registry_add(hashtable); \
return 1; \
} \
PRINTF("Failed to allocate %zu for the hashtable %s", memory_size, hashtable->name); \
return 0; \
} \
\
/** \
* Hash the key, get an index in the hashtable, try compare-and-set. \
* If fails (not likely) try again with the next slot (linear probing) \
* continue until success or max_tries is hit \
*/ \
static int hashtable_## tokn ##_insert(hashtable_t *hashtable, const uint32_t key, const data_type data) \
{ \
const uint32_t hash = hashtable->hashfunction(key); \
const uint32_t index = hashtable_get_index(hashtable, hash); \
/* I can do this for the last slot too - I allocated max_tries more slots */ \
const uint32_t index_max = index+max_tries; \
uint32_t i; \
hashtable->__stat.insert++; \
for (i = index;i < index_max;i++) \
{ \
hashtable_## tokn ##_slot_t *slot = HASHTABLE_SLOT_ADDR(hashtable, tokn, i); \
uint32_t old_key = HASHTABLE_CMPXCHG(&slot->key, illegal_key, key); \
if (likely(old_key == illegal_key)) /* Success */ \
{ \
slot->data = data; \
return 1; \
} \
else \
{ \
hashtable->__stat.collision++; \
} \
} \
\
hashtable->__stat.insert_err++; \
return 0; \
} \
\
/** \
* Hash the key, get an index in the hashtable, find the relevant entry, \
* read the pointer, remove using atomic operation \
* Only one context is allowed to remove a specific entry \
*/ \
static int hashtable_## tokn ##_remove(hashtable_t *hashtable, const uint32_t key, data_type *data) \
{ \
const uint32_t hash = hashtable->hashfunction(key); \
const uint32_t index = hashtable_get_index(hashtable, hash); \
/* I can do this for the last slot too - I allocated max_tries more slots */ \
const uint32_t index_max = index+max_tries; \
uint32_t i; \
hashtable->__stat.remove++; \
for (i = index;i < index_max;i++) \
{ \
hashtable_## tokn ##_slot_t *slot = HASHTABLE_SLOT_ADDR(hashtable, tokn, i); \
uint32_t old_key = slot->key; \
if (likely(old_key == key)) \
{ \
if (data) \
{ \
*data = slot->data; \
} \
__sync_access(&slot->data) = illegal_data; \
HASHTABLE_BARRIER(); \
__sync_access(&slot->key) = illegal_key; \
return 1; \
} \
} \
\
hashtable->__stat.remove_err++; \
return 0; \
} \
\
/** \
* Hash the key, get an index in the hashtable, find the relevant entry, \
* read the pointer \
*/ \
static int hashtable_## tokn ##_find(hashtable_t *hashtable, const uint32_t key, data_type *data) \
{ \
const uint32_t hash = hashtable->hashfunction(key); \
const uint32_t index = hashtable_get_index(hashtable, hash); \
/* I can do this for the last slot too - I allocated max_tries more slots */ \
const uint32_t index_max = index+max_tries; \
uint32_t i; \
hashtable->__stat.search++; \
for (i = index;i < index_max;i++) \
{ \
hashtable_## tokn ##_slot_t *slot = HASHTABLE_SLOT_ADDR(hashtable, tokn, i); \
uint32_t old_key = slot->key; \
if (old_key == key) \
{ \
*data = slot->data; \
return 1; \
} \
} \
\
return 0; \
} \
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