1 /*****************************************************************************
2
3 Copyright (c) 2012, 2015, Oracle and/or its affiliates. All Rights Reserved.
4 Copyright (c) 2017, 2019, MariaDB Corporation.
5
6 This program is free software; you can redistribute it and/or modify it under
7 the terms of the GNU General Public License as published by the Free Software
8 Foundation; version 2 of the License.
9
10 This program is distributed in the hope that it will be useful, but WITHOUT
11 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
12 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
13
14 You should have received a copy of the GNU General Public License along with
15 this program; if not, write to the Free Software Foundation, Inc.,
16 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA
17
18 *****************************************************************************/
19
20 /**************************************************//**
21 @file include/ut0counter.h
22
23 Counter utility class
24
25 Created 2012/04/12 by Sunny Bains
26 *******************************************************/
27
28 #ifndef ut0counter_h
29 #define ut0counter_h
30
31 #include "os0thread.h"
32 #include "my_rdtsc.h"
33
34 /** CPU cache line size */
35 #ifdef CPU_LEVEL1_DCACHE_LINESIZE
36 # define CACHE_LINE_SIZE CPU_LEVEL1_DCACHE_LINESIZE
37 #else
38 # error CPU_LEVEL1_DCACHE_LINESIZE is undefined
39 #endif /* CPU_LEVEL1_DCACHE_LINESIZE */
40
41 /** Default number of slots to use in ib_counter_t */
42 #define IB_N_SLOTS 64
43
44 /** Use the result of my_timer_cycles(), which mainly uses RDTSC for cycles
45 as a random value. See the comments for my_timer_cycles() */
46 /** @return result from RDTSC or similar functions. */
47 static inline size_t
get_rnd_value()48 get_rnd_value()
49 {
50 size_t c = static_cast<size_t>(my_timer_cycles());
51
52 if (c != 0) {
53 return c;
54 }
55
56 /* We may go here if my_timer_cycles() returns 0,
57 so we have to have the plan B for the counter. */
58 #if !defined(_WIN32)
59 return (size_t)os_thread_get_curr_id();
60 #else
61 LARGE_INTEGER cnt;
62 QueryPerformanceCounter(&cnt);
63
64 return static_cast<size_t>(cnt.QuadPart);
65 #endif /* !_WIN32 */
66 }
67
68 /** Class for using fuzzy counters. The counter is multi-instance relaxed atomic
69 so the results are not guaranteed to be 100% accurate but close
70 enough. Creates an array of counters and separates each element by the
71 CACHE_LINE_SIZE bytes */
72 template <typename Type, int N = IB_N_SLOTS>
73 struct ib_counter_t {
74 /** Increment the counter by 1. */
incib_counter_t75 void inc() { add(1); }
76
77 /** Increment the counter by 1.
78 @param[in] index a reasonably thread-unique identifier */
incib_counter_t79 void inc(size_t index) { add(index, 1); }
80
81 /** Add to the counter.
82 @param[in] n amount to be added */
addib_counter_t83 void add(Type n) { add(get_rnd_value(), n); }
84
85 /** Add to the counter.
86 @param[in] index a reasonably thread-unique identifier
87 @param[in] n amount to be added */
addib_counter_t88 void add(size_t index, Type n) {
89 index = index % N;
90
91 ut_ad(index < UT_ARR_SIZE(m_counter));
92
93 m_counter[index].value.fetch_add(n, std::memory_order_relaxed);
94 }
95
96 /* @return total value - not 100% accurate, since it is relaxed atomic*/
Typeib_counter_t97 operator Type() const {
98 Type total = 0;
99
100 for (const auto &counter : m_counter) {
101 total += counter.value.load(std::memory_order_relaxed);
102 }
103
104 return(total);
105 }
106
107 private:
108 /** Atomic which occupies whole CPU cache line.
109 Note: We rely on the default constructor of std::atomic and
110 do not explicitly initialize the contents. This works for us,
111 because ib_counter_t is only intended for usage with global
112 memory that is allocated from the .bss and thus guaranteed to
113 be zero-initialized by the run-time environment.
114 @see srv_stats
115 @see rw_lock_stats */
116 struct ib_counter_element_t {
117 MY_ALIGNED(CACHE_LINE_SIZE) std::atomic<Type> value;
118 };
119 static_assert(sizeof(ib_counter_element_t) == CACHE_LINE_SIZE, "");
120
121 /** Array of counter elements */
122 MY_ALIGNED(CACHE_LINE_SIZE) ib_counter_element_t m_counter[N];
123 };
124
125 #endif /* ut0counter_h */
126