* [B.A.T.M.A.N.] [PATCH 2/2] alfred: Use bitmap to store dataset change events
2017-07-24 21:18 [B.A.T.M.A.N.] [PATCH 0/2] alfred: Use bitmap to store dataset change events Sven Eckelmann
2017-07-24 21:18 ` [B.A.T.M.A.N.] [PATCH 1/2] alfred: Use constant to define data type range Sven Eckelmann
@ 2017-07-24 21:18 ` Sven Eckelmann
2017-07-31 8:57 ` [B.A.T.M.A.N.] [PATCH 0/2] " Simon Wunderlich
2 siblings, 0 replies; 4+ messages in thread
From: Sven Eckelmann @ 2017-07-24 21:18 UTC (permalink / raw)
To: b.a.t.m.a.n; +Cc: Sven Eckelmann, Anatoliy Lapitskiy
The implementation for --update-command uses a double linked list to store
the detected modifications of datasets. This implementation requires 24
bytes (1 byte data type, 7 bytes padding, 16 bytes linked list pointers) on
amd64 for each element of the list. Each modified dataset type requires an
own list item. Each list item is allocated using malloc and therefore
additional overhead for the libc allocator information has also to be
stored next to it. The list head uses a similar amount of memory (16 byte
list pointers, 2 byte counter, 6 byte padding) but doesn't require
additional allocations.
The list based implementation provides information about modified dataset
type and the order in which these modifications were detected. But the
latter is not actually required fr --update-command and can therefore be
omitted.
A simple 256 bit wide storage element (32 bytes) is enough to keep the
required information when only the detected modified data types have to be
registered. BIT(i) is either 1 when dataset type i was modified or 0 when
no modification was detected. This removes the (de)allocation CPU + memory
overhead and avoids list searches when adding newly detected modifications.
Cc: Anatoliy Lapitskiy <anatoliy.lapitskiy@gmail.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
alfred.h | 4 +-
bitops.h | 379 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
main.c | 3 +-
server.c | 46 ++++----
4 files changed, 401 insertions(+), 31 deletions(-)
create mode 100644 bitops.h
diff --git a/alfred.h b/alfred.h
index 53d8b7a..d559d95 100644
--- a/alfred.h
+++ b/alfred.h
@@ -31,6 +31,7 @@
#include <time.h>
#include <sys/select.h>
#include <sys/types.h>
+#include "bitops.h"
#include "list.h"
#include "packet.h"
@@ -134,8 +135,7 @@ struct globals {
const char *unix_path;
const char *update_command;
- struct list_head changed_data_types;
- uint16_t changed_data_type_count; /* maximum is 256 */
+ DECLARE_BITMAP(changed_data_types, ALFRED_NUM_TYPES);
struct timespec if_check;
struct timespec sync_period;
diff --git a/bitops.h b/bitops.h
new file mode 100644
index 0000000..37ce7e8
--- /dev/null
+++ b/bitops.h
@@ -0,0 +1,379 @@
+/* Minimal Linux-like bit manipulation helper functions
+ * (reduced version for alfred)
+ *
+ * Copyright (c) 2012-2014, Sven Eckelmann <sven@narfation.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef __LINUX_LIKE_BITOPS_H__
+#define __LINUX_LIKE_BITOPS_H__
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+
+#if defined(__GNUC__)
+#define BITOPS_BUILTIN_USE 1
+#endif
+
+#if defined(_MSC_VER)
+#define __inline__ __inline
+#endif
+
+/**
+ * BITOPS_BUILD_BUG_ON - create "negative array" build error on expression
+ * @e: expression which is considered to be a "bug"
+ */
+#define BITOPS_BUILD_BUG_ON(e) ((void)sizeof(char[1 - 2 * !!(e)]))
+
+/**
+ * BITOPS_DIV_CEIL - calculate quotient of integer division (round up)
+ * @numerator: side effect free expression for numerator of division
+ * @denominator: side effect free expression for denominator of division
+ *
+ * numerator and denominator must be from a type which can store
+ * denominator + numerator without overflow. denominator must be larger than 0
+ * and numerator must be positive.
+ *
+ * WARNING @numerator expression must be side-effect free
+ */
+#define BITOPS_DIV_CEIL(numerator, denominator) \
+ (((numerator) + (denominator) - 1) / (denominator))
+
+/**
+ * BITS_PER_BYTE - number of bits per byte/char
+ */
+#define BITS_PER_BYTE 8
+
+/**
+ * BITS_PER_LONG - number of bits per long
+ */
+#define BITS_PER_LONG (sizeof(unsigned long) * BITS_PER_BYTE)
+
+/**
+ * BITS_TO_LONGS - return number of longs to save at least bit 0..(bits - 1)
+ * @bits: number of required bits
+ */
+#define BITS_TO_LONGS(bits) \
+ BITOPS_DIV_CEIL(bits, BITS_PER_LONG)
+
+/**
+ * DECLARE_BITMAP - declare bitmap to store at least bit 0..(bits -1)
+ * @bitmap: name for the new bitmap
+ * @bits: number of required bits
+ */
+#define DECLARE_BITMAP(bitmap, bits) \
+ unsigned long bitmap[BITS_TO_LONGS(bits)]
+
+/**
+ * BITMAP_FIRST_WORD_MASK - return unsigned long mask for least significant long
+ * @start: offset to first bits
+ *
+ * All bits which can be modified in the least significant unsigned long for
+ * offset @start in the bitmap will be set to 1. All other bits will be set to
+ * zero
+ */
+#define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) % BITS_PER_LONG))
+
+/**
+ * BITMAP_LAST_WORD_MASK - return unsigned long mask for most significant long
+ * @bits: number of bits in complete bitmap
+ *
+ * All bits which can be modified in the most significant unsigned long in the
+ * bitmap will be set to 1. All other bits will be set to zero
+ */
+#define BITMAP_LAST_WORD_MASK(bits) (~0UL >> (-(bits) % BITS_PER_LONG))
+
+/**
+ * bitops_ffs() - find (least significant) first set bit plus one
+ * @x: unsigned long to check
+ *
+ * Return: plus-one index of first set bit; zero when x is zero
+ */
+static __inline__ size_t bitops_ffs(unsigned long x)
+{
+#ifdef BITOPS_BUILTIN_USE
+ return __builtin_ffsl(x);
+#else
+ size_t i = 1;
+
+ BITOPS_BUILD_BUG_ON(BITS_PER_LONG != 32 && BITS_PER_LONG != 64);
+
+ if (x == 0)
+ return 0;
+
+ if (BITS_PER_LONG == 64) {
+ if ((0x00000000fffffffful & x) == 0) {
+ i += 32;
+ x >>= 32;
+ }
+ }
+
+ if ((0x0000fffful & x) == 0) {
+ i += 16;
+ x >>= 16;
+ }
+
+ if ((0x00fful & x) == 0) {
+ i += 8;
+ x >>= 8;
+ }
+
+ if ((0x0ful & x) == 0) {
+ i += 4;
+ x >>= 4;
+ }
+
+ if ((0x3ul & x) == 0) {
+ i += 2;
+ x >>= 2;
+ }
+
+ if ((0x1ul & x) == 0) {
+ i += 1;
+ x >>= 1;
+ }
+
+ return i;
+#endif
+}
+
+/**
+ * hweight32() - number of set bits in an uint32_t
+ * @x: uint32_t to sum up
+ *
+ * Return: number of set bits
+ */
+static __inline__ unsigned int hweight32(uint32_t x)
+{
+ static const uint32_t m1 = UINT32_C(0x55555555);
+ static const uint32_t m2 = UINT32_C(0x33333333);
+ static const uint32_t m4 = UINT32_C(0x0f0f0f0f);
+
+ /* x = (x & m1) + ((x >> 1) & m1); */
+ x -= (x >> 1) & m1;
+ x = (x & m2) + ((x >> 2) & m2);
+ x = (x + (x >> 4)) & m4;
+ x += x >> 8;
+ x += x >> 16;
+
+ return x & 0x3f;
+}
+
+/**
+ * hweight64() - number of set bits in an uint64_t
+ * @x: uint64_t to sum up
+ *
+ * Return: number of set bits
+ */
+static __inline__ unsigned int hweight64(uint64_t x)
+{
+ if (BITS_PER_LONG >= 64) {
+ static const uint64_t m1 = UINT64_C(0x5555555555555555);
+ static const uint64_t m2 = UINT64_C(0x3333333333333333);
+ static const uint64_t m4 = UINT64_C(0x0f0f0f0f0f0f0f0f);
+
+ /* x = (x & m1) + ((x >> 1) & m1); */
+ x -= (x >> 1) & m1;
+ x = (x & m2) + ((x >> 2) & m2);
+ x = (x + (x >> 4)) & m4;
+ x += x >> 8;
+ x += x >> 16;
+ x += x >> 32;
+
+ return x & 0x7f;
+ } else {
+ return hweight32((uint32_t)x) + hweight32((uint32_t)(x >> 32));
+ }
+}
+
+/**
+ * hweight_long() - number of set bits in an unsigned long
+ * @x: unsigned long to sum up
+ *
+ * Return: number of set bits
+ */
+static __inline__ unsigned int hweight_long(unsigned long x)
+{
+#ifdef BITOPS_BUILTIN_USE
+ return __builtin_popcountl(x);
+#else
+ size_t i;
+
+ if (BITS_PER_LONG == 64)
+ return hweight64((uint64_t)x);
+
+ if (BITS_PER_LONG == 32)
+ return hweight32((uint32_t)x);
+
+ for (i = 0; x; i++)
+ x &= x - 1;
+
+ return i;
+#endif
+}
+
+/**
+ * bitmap_zero() - Initializes bitmap with zero
+ * @bitmap: bitmap to modify
+ * @bits: number of bits
+ *
+ * Initializes all bits to zero. This also includes the overhead bits in the
+ * last unsigned long which will not be used.
+ */
+static __inline__ void bitmap_zero(unsigned long *bitmap, size_t bits)
+{
+ memset(bitmap, 0, BITS_TO_LONGS(bits) * sizeof(unsigned long));
+}
+
+/**
+ * set_bit() - Set bit in bitmap to one
+ * @bit: address of bit to modify
+ * @bitmap: bitmap to modify
+ */
+static __inline__ void set_bit(size_t bit, unsigned long *bitmap)
+{
+ size_t l = bit / BITS_PER_LONG;
+ size_t b = bit % BITS_PER_LONG;
+
+ bitmap[l] |= 1UL << b;
+}
+
+/**
+ * find_next_bit() - Find next set bit in bitmap
+ * @bitmap: bitmap to check
+ * @bits: number of bits in @bitmap
+ * @start: start of bits to check
+ *
+ * Checks the modifiable bits in the bitmap. The overhead bits in the last
+ * unsigned long will not be checked
+ *
+ * Return: bit position of next set bit, @bits when no set bit was found
+ */
+static __inline__ size_t find_next_bit(unsigned long *bitmap, size_t bits,
+ size_t start)
+{
+ size_t i;
+ size_t pos;
+ unsigned long t;
+ size_t l = BITS_TO_LONGS(bits);
+ size_t first_long = start / BITS_PER_LONG;
+ size_t long_lower = start - (start % BITS_PER_LONG);
+
+ if (start >= bits)
+ return bits;
+
+ t = bitmap[first_long] & BITMAP_FIRST_WORD_MASK(start);
+ for (i = first_long + 1; !t && i < l; i++) {
+ /* search until valid t is found */
+ long_lower += BITS_PER_LONG;
+ t = bitmap[i];
+ }
+
+ if (!t)
+ return bits;
+
+ pos = long_lower + bitops_ffs(t) - 1;
+ if (pos >= bits)
+ return bits;
+
+ return pos;
+}
+
+/**
+ * find_first_bit - Find first set bit in bitmap
+ * @bitmap: bitmap to check
+ * @bits: number of bits in @bitmap
+ *
+ * Checks the modifiable bits in the bitmap. The overhead bits in the last
+ * unsigned long will not be checked
+ *
+ * Return: bit position of fist set bit, @bits when no set bit was found
+ */
+#define find_first_bit(bitmap, bits) find_next_bit(bitmap, bits, 0)
+
+/**
+ * for_each_set_bit - iterate over set bits in bitmap
+ * @bit: current bit
+ * @bitmap: bitmap to iterate over
+ * @bits: number of bits in @bitmap
+ *
+ * WARNING expressions @bitmap and @bits must be side-effect free
+ */
+#define for_each_set_bit(bit, bitmap, bits) \
+ for (bit = find_first_bit(bitmap, bits); \
+ bit < (bits); \
+ bit = find_next_bit(bitmap, bits, bit + 1))
+
+/**
+ * bitmap_weight() - Calculate number of set bits in bitmap
+ * @bitmap: bitmap to sum up
+ * @bits: number of bits
+ *
+ * Sums the modifiable bits in the bitmap. The overhead bits in the last
+ * unsigned long will not summed up
+ *
+ * Return: number of set bits
+ */
+static __inline__ size_t bitmap_weight(const unsigned long *bitmap, size_t bits)
+{
+ size_t l = BITS_TO_LONGS(bits);
+ size_t i;
+ size_t sum = 0;
+
+ for (i = 0; i < l - 1; i++)
+ sum += hweight_long(bitmap[i]);
+
+ return sum + hweight_long(bitmap[l - 1] & BITMAP_LAST_WORD_MASK(bits));
+}
+
+/**
+ * bitmap_empty() - Check if no bit is set in bitmap
+ * @bitmap: bitmap to test
+ * @bits: number of bits
+ *
+ * Check the modifiable bits in the bitmap for zero. The overhead bits in the
+ * last unsigned long will not be checked
+ *
+ * Return: true when usable bits were all zero and false otherwise
+ */
+static __inline__ bool bitmap_empty(const unsigned long *bitmap, size_t bits)
+{
+ size_t l = BITS_TO_LONGS(bits);
+ size_t i;
+
+ for (i = 0; i < l - 1; i++) {
+ if (bitmap[i])
+ return false;
+ }
+
+ return !(bitmap[l - 1] & BITMAP_LAST_WORD_MASK(bits));
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __LINUX_LIKE_BITOPS_H__ */
diff --git a/main.c b/main.c
index ad6d081..cf1e460 100644
--- a/main.c
+++ b/main.c
@@ -202,8 +202,7 @@ static struct globals *alfred_init(int argc, char *argv[])
globals->update_command = NULL;
globals->sync_period.tv_sec = ALFRED_INTERVAL;
globals->sync_period.tv_nsec = 0;
- INIT_LIST_HEAD(&globals->changed_data_types);
- globals->changed_data_type_count = 0;
+ bitmap_zero(globals->changed_data_types, ALFRED_NUM_TYPES);
time_random_seed();
diff --git a/server.c b/server.c
index b6f0812..63a3b2a 100644
--- a/server.c
+++ b/server.c
@@ -37,6 +37,7 @@
#include <unistd.h>
#include <time.h>
#include "alfred.h"
+#include "bitops.h"
#include "batadv_query.h"
#include "hash.h"
#include "list.h"
@@ -139,23 +140,10 @@ static int set_best_server(struct globals *globals)
void changed_data_type(struct globals *globals, uint8_t arg)
{
- struct changed_data_type *data_type = NULL;
-
if (!globals->update_command)
return;
- list_for_each_entry(data_type, &globals->changed_data_types, list) {
- if (data_type->data_type == arg)
- return;
- }
-
- data_type = malloc(sizeof(*data_type));
- if (!data_type)
- return;
-
- data_type->data_type = arg;
- list_add(&data_type->list, &globals->changed_data_types);
- globals->changed_data_type_count++;
+ set_bit(arg, globals->changed_data_types);
}
static int purge_data(struct globals *globals)
@@ -343,20 +331,27 @@ static void execute_update_command(struct globals *globals)
pid_t script_pid;
size_t command_len;
char *command;
- struct changed_data_type *data_type, *is;
- /* data type is uint8_t, so 255 is maximum (3 chars)
- * space for appending + terminating null byte
+ size_t data_type;
+ size_t changed_data_type_count;
+ /* data type is limited by ALFRED_NUM_TYPES to 255 (3 chars), plus
+ * 1x space for appending + terminating null byte
*/
char buf[5];
- if (!globals->update_command || !globals->changed_data_type_count)
+ if (!globals->update_command)
+ return;
+
+ if (bitmap_empty(globals->changed_data_types, ALFRED_NUM_TYPES))
return;
+ changed_data_type_count = bitmap_weight(globals->changed_data_types,
+ ALFRED_NUM_TYPES);
+
/* length of script + 4 bytes per data type (space +3 chars)
* + 1 for terminating null byte
*/
command_len = strlen(globals->update_command);
- command_len += 4 * globals->changed_data_type_count + 1;
+ command_len += 4 * changed_data_type_count + 1;
command = malloc(command_len);
if (!command)
return;
@@ -364,17 +359,14 @@ static void execute_update_command(struct globals *globals)
strncpy(command, globals->update_command, command_len - 1);
command[command_len - 1] = '\0';
- list_for_each_entry_safe(data_type, is, &globals->changed_data_types,
- list) {
+ for_each_set_bit (data_type, globals->changed_data_types,
+ ALFRED_NUM_TYPES) {
/* append the datatype to command line */
- snprintf(buf, sizeof(buf), " %d", data_type->data_type);
+ snprintf(buf, sizeof(buf), " %zu", data_type);
strncat(command, buf, command_len - strlen(command) - 1);
-
- /* clean the list */
- list_del(&data_type->list);
- free(data_type);
}
- globals->changed_data_type_count = 0;
+
+ bitmap_zero(globals->changed_data_types, ALFRED_NUM_TYPES);
printf("executing: %s\n", command);
--
2.11.0
^ permalink raw reply related [flat|nested] 4+ messages in thread