| /* Implement a cached obstack. |
| Written by Fred Fish <fnf@cygnus.com> |
| Rewritten by Jim Blandy <jimb@cygnus.com> |
| |
| Copyright (C) 1999-2021 Free Software Foundation, Inc. |
| |
| This file is part of GDB. |
| |
| 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/>. */ |
| |
| #include "defs.h" |
| #include "gdb_obstack.h" |
| #include "bcache.h" |
| |
| #include <algorithm> |
| |
| namespace gdb { |
| |
| /* The type used to hold a single bcache string. The user data is |
| stored in d.data. Since it can be any type, it needs to have the |
| same alignment as the most strict alignment of any type on the host |
| machine. I don't know of any really correct way to do this in |
| stock ANSI C, so just do it the same way obstack.h does. */ |
| |
| struct bstring |
| { |
| /* Hash chain. */ |
| struct bstring *next; |
| /* Assume the data length is no more than 64k. */ |
| unsigned short length; |
| /* The half hash hack. This contains the upper 16 bits of the hash |
| value and is used as a pre-check when comparing two strings and |
| avoids the need to do length or memcmp calls. It proves to be |
| roughly 100% effective. */ |
| unsigned short half_hash; |
| |
| union |
| { |
| char data[1]; |
| double dummy; |
| } |
| d; |
| }; |
| |
| |
| /* Growing the bcache's hash table. */ |
| |
| /* If the average chain length grows beyond this, then we want to |
| resize our hash table. */ |
| #define CHAIN_LENGTH_THRESHOLD (5) |
| |
| void |
| bcache::expand_hash_table () |
| { |
| /* A table of good hash table sizes. Whenever we grow, we pick the |
| next larger size from this table. sizes[i] is close to 1 << (i+10), |
| so we roughly double the table size each time. After we fall off |
| the end of this table, we just double. Don't laugh --- there have |
| been executables sighted with a gigabyte of debug info. */ |
| static unsigned long sizes[] = { |
| 1021, 2053, 4099, 8191, 16381, 32771, |
| 65537, 131071, 262144, 524287, 1048573, 2097143, |
| 4194301, 8388617, 16777213, 33554467, 67108859, 134217757, |
| 268435459, 536870923, 1073741827, 2147483659UL |
| }; |
| unsigned int new_num_buckets; |
| struct bstring **new_buckets; |
| unsigned int i; |
| |
| /* Count the stats. Every unique item needs to be re-hashed and |
| re-entered. */ |
| m_expand_count++; |
| m_expand_hash_count += m_unique_count; |
| |
| /* Find the next size. */ |
| new_num_buckets = m_num_buckets * 2; |
| for (i = 0; i < (sizeof (sizes) / sizeof (sizes[0])); i++) |
| if (sizes[i] > m_num_buckets) |
| { |
| new_num_buckets = sizes[i]; |
| break; |
| } |
| |
| /* Allocate the new table. */ |
| { |
| size_t new_size = new_num_buckets * sizeof (new_buckets[0]); |
| |
| new_buckets = (struct bstring **) xmalloc (new_size); |
| memset (new_buckets, 0, new_size); |
| |
| m_structure_size -= m_num_buckets * sizeof (m_bucket[0]); |
| m_structure_size += new_size; |
| } |
| |
| /* Rehash all existing strings. */ |
| for (i = 0; i < m_num_buckets; i++) |
| { |
| struct bstring *s, *next; |
| |
| for (s = m_bucket[i]; s; s = next) |
| { |
| struct bstring **new_bucket; |
| next = s->next; |
| |
| new_bucket = &new_buckets[(this->hash (&s->d.data, s->length) |
| % new_num_buckets)]; |
| s->next = *new_bucket; |
| *new_bucket = s; |
| } |
| } |
| |
| /* Plug in the new table. */ |
| xfree (m_bucket); |
| m_bucket = new_buckets; |
| m_num_buckets = new_num_buckets; |
| } |
| |
| |
| /* Looking up things in the bcache. */ |
| |
| /* The number of bytes needed to allocate a struct bstring whose data |
| is N bytes long. */ |
| #define BSTRING_SIZE(n) (offsetof (struct bstring, d.data) + (n)) |
| |
| /* Find a copy of the LENGTH bytes at ADDR in BCACHE. If BCACHE has |
| never seen those bytes before, add a copy of them to BCACHE. In |
| either case, return a pointer to BCACHE's copy of that string. If |
| optional ADDED is not NULL, return 1 in case of new entry or 0 if |
| returning an old entry. */ |
| |
| const void * |
| bcache::insert (const void *addr, int length, bool *added) |
| { |
| unsigned long full_hash; |
| unsigned short half_hash; |
| int hash_index; |
| struct bstring *s; |
| |
| if (added != nullptr) |
| *added = false; |
| |
| /* Lazily initialize the obstack. This can save quite a bit of |
| memory in some cases. */ |
| if (m_total_count == 0) |
| { |
| /* We could use obstack_specify_allocation here instead, but |
| gdb_obstack.h specifies the allocation/deallocation |
| functions. */ |
| obstack_init (&m_cache); |
| } |
| |
| /* If our average chain length is too high, expand the hash table. */ |
| if (m_unique_count >= m_num_buckets * CHAIN_LENGTH_THRESHOLD) |
| expand_hash_table (); |
| |
| m_total_count++; |
| m_total_size += length; |
| |
| full_hash = this->hash (addr, length); |
| |
| half_hash = (full_hash >> 16); |
| hash_index = full_hash % m_num_buckets; |
| |
| /* Search the hash m_bucket for a string identical to the caller's. |
| As a short-circuit first compare the upper part of each hash |
| values. */ |
| for (s = m_bucket[hash_index]; s; s = s->next) |
| { |
| if (s->half_hash == half_hash) |
| { |
| if (s->length == length |
| && this->compare (&s->d.data, addr, length)) |
| return &s->d.data; |
| else |
| m_half_hash_miss_count++; |
| } |
| } |
| |
| /* The user's string isn't in the list. Insert it after *ps. */ |
| { |
| struct bstring *newobj |
| = (struct bstring *) obstack_alloc (&m_cache, |
| BSTRING_SIZE (length)); |
| |
| memcpy (&newobj->d.data, addr, length); |
| newobj->length = length; |
| newobj->next = m_bucket[hash_index]; |
| newobj->half_hash = half_hash; |
| m_bucket[hash_index] = newobj; |
| |
| m_unique_count++; |
| m_unique_size += length; |
| m_structure_size += BSTRING_SIZE (length); |
| |
| if (added != nullptr) |
| *added = true; |
| |
| return &newobj->d.data; |
| } |
| } |
| |
| |
| /* See bcache.h. */ |
| |
| unsigned long |
| bcache::hash (const void *addr, int length) |
| { |
| return fast_hash (addr, length, 0); |
| } |
| |
| /* See bcache.h. */ |
| |
| int |
| bcache::compare (const void *left, const void *right, int length) |
| { |
| return memcmp (left, right, length) == 0; |
| } |
| |
| /* Free all the storage associated with BCACHE. */ |
| bcache::~bcache () |
| { |
| /* Only free the obstack if we actually initialized it. */ |
| if (m_total_count > 0) |
| obstack_free (&m_cache, 0); |
| xfree (m_bucket); |
| } |
| |
| |
| |
| /* Printing statistics. */ |
| |
| static void |
| print_percentage (int portion, int total) |
| { |
| if (total == 0) |
| /* i18n: Like "Percentage of duplicates, by count: (not applicable)". */ |
| printf_filtered (_("(not applicable)\n")); |
| else |
| printf_filtered ("%3d%%\n", (int) (portion * 100.0 / total)); |
| } |
| |
| |
| /* Print statistics on BCACHE's memory usage and efficacity at |
| eliminating duplication. NAME should describe the kind of data |
| BCACHE holds. Statistics are printed using `printf_filtered' and |
| its ilk. */ |
| void |
| bcache::print_statistics (const char *type) |
| { |
| int occupied_buckets; |
| int max_chain_length; |
| int median_chain_length; |
| int max_entry_size; |
| int median_entry_size; |
| |
| /* Count the number of occupied buckets, tally the various string |
| lengths, and measure chain lengths. */ |
| { |
| unsigned int b; |
| int *chain_length = XCNEWVEC (int, m_num_buckets + 1); |
| int *entry_size = XCNEWVEC (int, m_unique_count + 1); |
| int stringi = 0; |
| |
| occupied_buckets = 0; |
| |
| for (b = 0; b < m_num_buckets; b++) |
| { |
| struct bstring *s = m_bucket[b]; |
| |
| chain_length[b] = 0; |
| |
| if (s) |
| { |
| occupied_buckets++; |
| |
| while (s) |
| { |
| gdb_assert (b < m_num_buckets); |
| chain_length[b]++; |
| gdb_assert (stringi < m_unique_count); |
| entry_size[stringi++] = s->length; |
| s = s->next; |
| } |
| } |
| } |
| |
| /* To compute the median, we need the set of chain lengths |
| sorted. */ |
| std::sort (chain_length, chain_length + m_num_buckets); |
| std::sort (entry_size, entry_size + m_unique_count); |
| |
| if (m_num_buckets > 0) |
| { |
| max_chain_length = chain_length[m_num_buckets - 1]; |
| median_chain_length = chain_length[m_num_buckets / 2]; |
| } |
| else |
| { |
| max_chain_length = 0; |
| median_chain_length = 0; |
| } |
| if (m_unique_count > 0) |
| { |
| max_entry_size = entry_size[m_unique_count - 1]; |
| median_entry_size = entry_size[m_unique_count / 2]; |
| } |
| else |
| { |
| max_entry_size = 0; |
| median_entry_size = 0; |
| } |
| |
| xfree (chain_length); |
| xfree (entry_size); |
| } |
| |
| printf_filtered (_(" M_Cached '%s' statistics:\n"), type); |
| printf_filtered (_(" Total object count: %ld\n"), m_total_count); |
| printf_filtered (_(" Unique object count: %lu\n"), m_unique_count); |
| printf_filtered (_(" Percentage of duplicates, by count: ")); |
| print_percentage (m_total_count - m_unique_count, m_total_count); |
| printf_filtered ("\n"); |
| |
| printf_filtered (_(" Total object size: %ld\n"), m_total_size); |
| printf_filtered (_(" Unique object size: %ld\n"), m_unique_size); |
| printf_filtered (_(" Percentage of duplicates, by size: ")); |
| print_percentage (m_total_size - m_unique_size, m_total_size); |
| printf_filtered ("\n"); |
| |
| printf_filtered (_(" Max entry size: %d\n"), max_entry_size); |
| printf_filtered (_(" Average entry size: ")); |
| if (m_unique_count > 0) |
| printf_filtered ("%ld\n", m_unique_size / m_unique_count); |
| else |
| /* i18n: "Average entry size: (not applicable)". */ |
| printf_filtered (_("(not applicable)\n")); |
| printf_filtered (_(" Median entry size: %d\n"), median_entry_size); |
| printf_filtered ("\n"); |
| |
| printf_filtered (_(" \ |
| Total memory used by bcache, including overhead: %ld\n"), |
| m_structure_size); |
| printf_filtered (_(" Percentage memory overhead: ")); |
| print_percentage (m_structure_size - m_unique_size, m_unique_size); |
| printf_filtered (_(" Net memory savings: ")); |
| print_percentage (m_total_size - m_structure_size, m_total_size); |
| printf_filtered ("\n"); |
| |
| printf_filtered (_(" Hash table size: %3d\n"), |
| m_num_buckets); |
| printf_filtered (_(" Hash table expands: %lu\n"), |
| m_expand_count); |
| printf_filtered (_(" Hash table hashes: %lu\n"), |
| m_total_count + m_expand_hash_count); |
| printf_filtered (_(" Half hash misses: %lu\n"), |
| m_half_hash_miss_count); |
| printf_filtered (_(" Hash table population: ")); |
| print_percentage (occupied_buckets, m_num_buckets); |
| printf_filtered (_(" Median hash chain length: %3d\n"), |
| median_chain_length); |
| printf_filtered (_(" Average hash chain length: ")); |
| if (m_num_buckets > 0) |
| printf_filtered ("%3lu\n", m_unique_count / m_num_buckets); |
| else |
| /* i18n: "Average hash chain length: (not applicable)". */ |
| printf_filtered (_("(not applicable)\n")); |
| printf_filtered (_(" Maximum hash chain length: %3d\n"), |
| max_chain_length); |
| printf_filtered ("\n"); |
| } |
| |
| int |
| bcache::memory_used () |
| { |
| if (m_total_count == 0) |
| return 0; |
| return obstack_memory_used (&m_cache); |
| } |
| |
| } /* namespace gdb */ |