/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
* Copyright by the Board of Trustees of the University of Illinois. *
* All rights reserved. *
* *
* This file is part of HDF5. The full HDF5 copyright notice, including *
* terms governing use, modification, and redistribution, is contained in *
* the files COPYING and Copyright.html. COPYING can be found at the root *
* of the source code distribution tree; Copyright.html can be found at the *
* root level of an installed copy of the electronic HDF5 document set and *
* is linked from the top-level documents page. It can also be found at *
* http://hdf.ncsa.uiuc.edu/HDF5/doc/Copyright.html. If you do not have *
* access to either file, you may request a copy from hdfhelp@ncsa.uiuc.edu. *
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
/*
* Programmer: John Mainzer -- 10/12/04
*
* Purpose: This file contains declarations which are normally visible
* only within the H5C package (just H5C.c at present).
*
* Source files outside the H5C package should include
* H5Cprivate.h instead.
*
* The one exception to this rule is test/cache.c. The test
* code is easier to write if it can look at the cache's
* internal data structures. Indeed, this is the main
* reason why this file was created.
*/
#ifndef H5C_PACKAGE
#error "Do not include this file outside the H5HL package!"
#endif
#ifndef _H5Cpkg_H
#define _H5Cpkg_H
/* Get package's private header */
#include "H5Cprivate.h"
/* Get needed headers */
#include "H5SLprivate.h" /* Skip lists */
#define H5C__HASH_TABLE_LEN (64 * 1024) /* must be a power of 2 */
/****************************************************************************
*
* structure H5C_t
*
* Catchall structure for all variables specific to an instance of the cache.
*
* While the individual fields of the structure are discussed below, the
* following overview may be helpful.
*
* Entries in the cache are stored in an instance of H5TB_TREE, indexed on
* the entry's disk address. While the H5TB_TREE is less efficient than
* hash table, it keeps the entries in address sorted order. As flushes
* in parallel mode are more efficient if they are issued in increasing
* address order, this is a significant benefit. Also the H5TB_TREE code
* was readily available, which reduced development time.
*
* While the cache was designed with multiple replacement policies in mind,
* at present only a modified form of LRU is supported.
*
* JRM - 4/26/04
*
* Profiling has indicated that searches in the instance of H5TB_TREE are
* too expensive. To deal with this issue, I have augmented the cache
* with a hash table in which all entries will be stored. Given the
* advantages of flushing entries in increasing address order, the TBBT
* is retained, but only dirty entries are stored in it. At least for
* now, we will leave entries in the TBBT after they are flushed.
*
* Note that index_size and index_len now refer to the total size of
* and number of entries in the hash table.
*
* JRM - 7/19/04
*
* magic: Unsigned 32 bit integer always set to H5C__H5C_T_MAGIC. This
* field is used to validate pointers to instances of H5C_t.
*
* max_type_id: Integer field containing the maximum type id number assigned
* to a type of entry in the cache. All type ids from 0 to
* max_type_id inclusive must be defined. The names of the
* types are stored in the type_name_table discussed below, and
* indexed by the ids.
*
* type_name_table_ptr: Pointer to an array of pointer to char of length
* max_type_id + 1. The strings pointed to by the entries
* in the array are the names of the entry types associated
* with the indexing type IDs.
*
* max_cache_size: Nominal maximum number of bytes that may be stored in the
* cache. This value should be viewed as a soft limit, as the
* cache can exceed this value under the following circumstances:
*
* a) All entries in the cache are protected, and the cache is
* asked to insert a new entry. In this case the new entry
* will be created. If this causes the cache to exceed
* max_cache_size, it will do so. The cache will attempt
* to reduce its size as entries are unprotected.
*
* b) When running in parallel mode, the cache may not be
* permitted to flush a dirty entry in response to a read.
* If there are no clean entries available to evict, the
* cache will exceed its maximum size. Again the cache
* will attempt to reduce its size to the max_cache_size
* limit on the next cache write.
*
* min_clean_size: Nominal minimum number of clean bytes in the cache.
* The cache attempts to maintain this number of bytes of
* clean data so as to avoid case b) above. Again, this is
* a soft limit.
*
*
* In addition to the call back functions required for each entry, the
* cache requires the following call back functions for this instance of
* the cache as a whole:
*
* check_write_permitted: In certain applications, the cache may not
* be allowed to write to disk at certain time. If specified,
* the check_write_permitted function is used to determine if
* a write is permissible at any given point in time.
*
* If no such function is specified (i.e. this field is NULL),
* the cache will presume that writes are always permissable.
*
*
* The cache requires an index to facilitate searching for entries. The
* following fields support that index.
*
* index_len: Number of entries currently in the hash table used to index
* the cache.
*
* index_size: Number of bytes of cache entries currently stored in the
* hash table used to index the cache.
*
* This value should not be mistaken for footprint of the
* cache in memory. The average cache entry is small, and
* the cache has a considerable overhead. Multiplying the
* index_size by two should yield a conservative estimate
* of the cache's memory footprint.
*
* index: Array of pointer to H5C_cache_entry_t of size
* H5C__HASH_TABLE_LEN. At present, this value is a power
* of two, not the usual prime number.
*
* I hope that the variable size of cache elements, the large
* hash table size, and the way in which HDF5 allocates space
* will combine to avoid problems with periodicity. If so, we
* can use a trivial hash function (a bit-and and a 3 bit left
* shift) with some small savings.
*
* If not, it will become evident in the statistics. Changing
* to the usual prime number length hash table will require
* changing the H5C__HASH_FCN macro and the deletion of the
* H5C__HASH_MASK #define. No other changes should be required.
*
*
* When we flush the cache, we need to write entries out in increasing
* address order. An instance of a skip list is used to store dirty entries in
* sorted order. Whether it is cheaper to sort the dirty entries as needed,
* or to maintain the list is an open question. At a guess, it depends
* on how frequently the cache is flushed. We will see how it goes.
*
* For now at least, I will not remove dirty entries from the list as they
* are flushed.
*
* slist_len: Number of entries currently in the skip list
* used to maintain a sorted list of dirty entries in the
* cache.
*
* slist_size: Number of bytes of cache entries currently stored in the
* skip list used to maintain a sorted list of
* dirty entries in the cache.
*
* slist_ptr: pointer to the instance of H5SL_t used maintain a sorted
* list of dirty entries in the cache. This sorted list has
* two uses:
*
* a) It allows us to flush dirty entries in increasing address
* order, which results in significant savings.
*
* b) It facilitates checking for adjacent dirty entries when
* attempting to evict entries from the cache. While we
* don't use this at present, I hope that this will allow
* some optimizations when I get to it.
*
*
* When a cache entry is protected, it must be removed from the LRU
* list(s) as it cannot be either flushed or evicted until it is unprotected.
* The following fields are used to implement the protected list (pl).
*
* pl_len: Number of entries currently residing on the protected list.
*
* pl_size: Number of bytes of cache entries currently residing on the
* protected list.
*
* pl_head_ptr: Pointer to the head of the doubly linked list of protected
* entries. Note that cache entries on this list are linked
* by their next and prev fields.
*
* This field is NULL if the list is empty.
*
* pl_tail_ptr: Pointer to the tail of the doubly linked list of protected
* entries. Note that cache entries on this list are linked
* by their next and prev fields.
*
* This field is NULL if the list is empty.
*
*
* The cache must have a replacement policy, and the fields supporting this
* policy must be accessible from this structure.
*
* While there has been interest in several replacement policies for
* this cache, the initial development schedule is tight. Thus I have
* elected to support only a modified LRU policy for the first cut.
*
* To further simplify matters, I have simply included the fields needed
* by the modified LRU in this structure. When and if we add support for
* other policies, it will probably be easiest to just add the necessary
* fields to this structure as well -- we only create one instance of this
* structure per file, so the overhead is not excessive.
*
*
* Fields supporting the modified LRU policy:
*
* See most any OS text for a discussion of the LRU replacement policy.
*
* When operating in parallel mode, we must ensure that a read does not
* cause a write. If it does, the process will hang, as the write will
* be collective and the other processes will not know to participate.
*
* To deal with this issue, I have modified the usual LRU policy by adding
* clean and dirty LRU lists to the usual LRU list.
*
* The clean LRU list is simply the regular LRU list with all dirty cache
* entries removed.
*
* Similarly, the dirty LRU list is the regular LRU list with all the clean
* cache entries removed.
*
* When reading in parallel mode, we evict from the clean LRU list only.
* This implies that we must try to ensure that the clean LRU list is
* reasonably well stocked at all times.
*
* We attempt to do this by trying to flush enough entries on each write
* to keep the cLRU_list_size >= min_clean_size.
*
* Even if we start with a completely clean cache, a sequence of protects
* without unprotects can empty the clean LRU list. In this case, the
* cache must grow temporarily. At the next write, we will attempt to
* evict enough entries to reduce index_size to less than max_cache_size.
* While this will usually be possible, all bets are off if enough entries
* are protected.
*
* Discussions of the individual fields used by the modified LRU replacement
* policy follow:
*
* LRU_list_len: Number of cache entries currently on the LRU list.
*
* Observe that LRU_list_len + pl_len must always equal
* index_len.
*
* LRU_list_size: Number of bytes of cache entries currently residing on the
* LRU list.
*
* Observe that LRU_list_size + pl_size must always equal
* index_size.
*
* LRU_head_ptr: Pointer to the head of the doubly linked LRU list. Cache
* entries on this list are linked by their next and prev fields.
*
* This field is NULL if the list is empty.
*
* LRU_tail_ptr: Pointer to the tail of the doubly linked LRU list. Cache
* entries on this list are linked by their next and prev fields.
*
* This field is NULL if the list is empty.
*
* cLRU_list_len: Number of cache entries currently on the clean LRU list.
*
* Observe that cLRU_list_len + dLRU_list_len must always
* equal LRU_list_len.
*
* cLRU_list_size: Number of bytes of cache entries currently residing on
* the clean LRU list.
*
* Observe that cLRU_list_size + dLRU_list_size must always
* equal LRU_list_size.
*
* cLRU_head_ptr: Pointer to the head of the doubly linked clean LRU list.
* Cache entries on this list are linked by their aux_next and
* aux_prev fields.
*
* This field is NULL if the list is empty.
*
* cLRU_tail_ptr: Pointer to the tail of the doubly linked clean LRU list.
* Cache entries on this list are linked by their aux_next and
* aux_prev fields.
*
* This field is NULL if the list is empty.
*
* dLRU_list_len: Number of cache entries currently on the dirty LRU list.
*
* Observe that cLRU_list_len + dLRU_list_len must always
* equal LRU_list_len.
*
* dLRU_list_size: Number of cache entries currently on the dirty LRU list.
*
* Observe that cLRU_list_len + dLRU_list_len must always
* equal LRU_list_len.
*
* dLRU_head_ptr: Pointer to the head of the doubly linked dirty LRU list.
* Cache entries on this list are linked by their aux_next and
* aux_prev fields.
*
* This field is NULL if the list is empty.
*
* dLRU_tail_ptr: Pointer to the tail of the doubly linked dirty LRU list.
* Cache entries on this list are linked by their aux_next and
* aux_prev fields.
*
* This field is NULL if the list is empty.
*
*
* Automatic cache size adjustment:
*
* While the default cache size is adequate for most cases, we can run into
* cases where the default is too small. Ideally, we will let the user
* adjust the cache size as required. However, this is not possible in all
* cases. Thus I have added automatic cache size adjustment code.
*
* The configuration for the automatic cache size adjustment is stored in
* the structure described below:
*
* size_increase_possible: Depending on the configuration data given
* in the resize_ctl field, it may or may not be possible
* to increase the size of the cache. Rather than test for
* all the ways this can happen, we simply set this flag when
* we receive a new configuration.
*
* size_decrease_possible: Depending on the configuration data given
* in the resize_ctl field, it may or may not be possible
* to decrease the size of the cache. Rather than test for
* all the ways this can happen, we simply set this flag when
* we receive a new configuration.
*
* cache_full: Boolean flag used to keep track of whether the cache is
* full, so we can refrain from increasing the size of a
* cache which hasn't used up the space alotted to it.
*
* The field is initialized to FALSE, and then set to TRUE
* whenever we attempt to make space in the cache.
*
* resize_enabled: This is another convenience flag which is set whenever
* a new set of values for resize_ctl are provided. Very
* simply,
*
* resize_enabled = size_increase_possible ||
* size_decrease_possible;
*
* size_decreased: Boolean flag set to TRUE whenever the maximun cache
* size is decreased. The flag triggers a call to
* H5C_make_space_in_cache() on the next call to H5C_protect().
*
* resize_ctl: Instance of H5C_auto_size_ctl_t containing configuration
* data for automatic cache resizing.
*
* epoch_markers_active: Integer field containing the number of epoch
* markers currently in use in the LRU list. This value
* must be in the range [0, H5C__MAX_EPOCH_MARKERS - 1].
*
* epoch_marker_active: Array of boolean of length H5C__MAX_EPOCH_MARKERS.
* This array is used to track which epoch markers are currently
* in use.
*
* epoch_marker_ringbuf: Array of int of length H5C__MAX_EPOCH_MARKERS + 1.
*
* To manage the epoch marker cache entries, it is necessary
* to track their order in the LRU list. This is done with
* epoch_marker_ringbuf. When markers are inserted at the
* head of the LRU list, the index of the marker in the
* epoch_markers array is inserted at the tail of the ring
* buffer. When it becomes the epoch_marker_active'th marker
* in the LRU list, it will have worked its way to the head
* of the ring buffer as well. This allows us to remove it
* without scanning the LRU list if such is required.
*
* epoch_marker_ringbuf_first: Integer field containing the index of the
* first entry in the ring buffer.
*
* epoch_marker_ringbuf_last: Integer field containing the index of the
* last entry in the ring buffer.
*
* epoch_marker_ringbuf_size: Integer field containing the number of entries
* in the ring buffer.
*
* epoch_markers: Array of instances of H5C_cache_entry_t of length
* H5C__MAX_EPOCH_MARKERS. The entries are used as markers
* in the LRU list to identify cache entries that haven't
* been accessed for some (small) specified number of
* epochs. These entries (if any) can then be evicted and
* the cache size reduced -- ideally without evicting any
* of the current working set. Needless to say, the epoch
* length and the number of epochs before an unused entry
* must be chosen so that all, or almost all, the working
* set will be accessed before the limit.
*
* Epoch markers only appear in the LRU list, never in
* the index or slist. While they are of type
* H5C__EPOCH_MARKER_TYPE, and have associated class
* functions, these functions should never be called.
*
* The addr fields of these instances of H5C_cache_entry_t
* are set to the index of the instance in the epoch_markers
* array, the size is set to 0, and the type field points
* to the constant structure epoch_marker_class defined
* in H5C.c. The next and prev fields are used as usual
* to link the entry into the LRU list.
*
* All other fields are unused.
*
*
* Cache hit rate collection fields:
*
* We supply the current cache hit rate on request, so we must keep a
* simple cache hit rate computation regardless of whether statistics
* collection is enabled. The following fields support this capability.
*
* cache_hits: Number of cache hits since the last time the cache hit
* rate statistics were reset. Note that when automatic cache
* re-sizing is enabled, this field will be reset every automatic
* resize epoch.
*
* cache_accesses: Number of times the cache has been accessed while
* since the last since the last time the cache hit rate statistics
* were reset. Note that when automatic cache re-sizing is enabled,
* this field will be reset every automatic resize epoch.
*
*
* Statistics collection fields:
*
* When enabled, these fields are used to collect statistics as described
* below. The first set are collected only when H5C_COLLECT_CACHE_STATS
* is true.
*
* hits: Array of int64 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the number of times an entry with type id
* equal to the array index has been in cache when requested in
* the current epoch.
*
* misses: Array of int64 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the number of times an entry with type id
* equal to the array index has not been in cache when
* requested in the current epoch.
*
* insertions: Array of int64 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the number of times an entry with type
* id equal to the array index has been inserted into the
* cache in the current epoch.
*
* clears: Array of int64 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the number of times an entry with type
* id equal to the array index has been cleared in the current
* epoch.
*
* flushes: Array of int64 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the number of times an entry with type id
* equal to the array index has been written to disk in the
* current epoch.
*
* evictions: Array of int64 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the number of times an entry with type id
* equal to the array index has been evicted from the cache in
* the current epoch.
*
* renames: Array of int64 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the number of times an entry with type
* id equal to the array index has been renamed in the current
* epoch.
*
* total_ht_insertions: Number of times entries have been inserted into the
* hash table in the current epoch.
*
* total_ht_deletions: Number of times entries have been deleted from the
* hash table in the current epoch.
*
* successful_ht_searches: int64 containing the total number of successful
* searches of the hash table in the current epoch.
*
* total_successful_ht_search_depth: int64 containing the total number of
* entries other than the targets examined in successful
* searches of the hash table in the current epoch.
*
* failed_ht_searches: int64 containing the total number of unsuccessful
* searches of the hash table in the current epoch.
*
* total_failed_ht_search_depth: int64 containing the total number of
* entries examined in unsuccessful searches of the hash
* table in the current epoch.
*
* max_index_len: Largest value attained by the index_len field in the
* current epoch.
*
* max_index_size: Largest value attained by the index_size field in the
* current epoch.
*
* max_slist_len: Largest value attained by the slist_len field in the
* current epoch.
*
* max_slist_size: Largest value attained by the slist_size field in the
* current epoch.
*
* max_pl_len: Largest value attained by the pl_len field in the
* current epoch.
*
* max_pl_size: Largest value attained by the pl_size field in the
* current epoch.
*
* The remaining stats are collected only when both H5C_COLLECT_CACHE_STATS
* and H5C_COLLECT_CACHE_ENTRY_STATS are true.
*
* max_accesses: Array of int32 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the maximum number of times any single
* entry with type id equal to the array index has been
* accessed in the current epoch.
*
* min_accesses: Array of int32 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the minimum number of times any single
* entry with type id equal to the array index has been
* accessed in the current epoch.
*
* max_clears: Array of int32 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the maximum number of times any single
* entry with type id equal to the array index has been cleared
* in the current epoch.
*
* max_flushes: Array of int32 of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the maximum number of times any single
* entry with type id equal to the array index has been
* flushed in the current epoch.
*
* max_size: Array of size_t of length H5C__MAX_NUM_TYPE_IDS + 1. The cells
* are used to record the maximum size of any single entry
* with type id equal to the array index that has resided in
* the cache in the current epoch.
*
*
* Fields supporting testing:
*
* For test purposes, it is useful to turn off some asserts and sanity
* checks. The following flags support this.
*
* skip_file_checks: Boolean flag used to skip sanity checks on file
* parameters passed to the cache. In the test bed, there
* is no reason to have a file open, as the cache proper
* just passes these parameters through without using them.
*
* When this flag is set, all sanity checks on the file
* parameters are skipped. The field defaults to FALSE.
*
* skip_dxpl_id_checks: Boolean flag used to skip sanity checks on the
* dxpl_id parameters passed to the cache. These are not
* used directly by the cache, so skipping the checks
* simplifies the test bed.
*
* When this flag is set, all sanity checks on the dxpl_id
* parameters are skipped. The field defaults to FALSE.
*
****************************************************************************/
#define H5C__H5C_T_MAGIC 0x005CAC0E
#define H5C__MAX_NUM_TYPE_IDS 10
#define H5C__MAX_EPOCH_MARKERS 10
struct H5C_t
{
uint32_t magic;
int32_t max_type_id;
const char * (* type_name_table_ptr);
size_t max_cache_size;
size_t min_clean_size;
H5C_write_permitted_func_t check_write_permitted;
int32_t index_len;
size_t index_size;
H5C_cache_entry_t * (index[H5C__HASH_TABLE_LEN]);
int32_t slist_len;
size_t slist_size;
H5SL_t * slist_ptr;
int32_t pl_len;
size_t pl_size;
H5C_cache_entry_t * pl_head_ptr;
H5C_cache_entry_t * pl_tail_ptr;
int32_t LRU_list_len;
size_t LRU_list_size;
H5C_cache_entry_t * LRU_head_ptr;
H5C_cache_entry_t * LRU_tail_ptr;
int32_t cLRU_list_len;
size_t cLRU_list_size;
H5C_cache_entry_t * cLRU_head_ptr;
H5C_cache_entry_t * cLRU_tail_ptr;
int32_t dLRU_list_len;
size_t dLRU_list_size;
H5C_cache_entry_t * dLRU_head_ptr;
H5C_cache_entry_t * dLRU_tail_ptr;
hbool_t size_increase_possible;
hbool_t size_decrease_possible;
hbool_t resize_enabled;
hbool_t cache_full;
hbool_t size_decreased;
H5C_auto_size_ctl_t resize_ctl;
int32_t epoch_markers_active;
hbool_t epoch_marker_active[H5C__MAX_EPOCH_MARKERS];
int32_t epoch_marker_ringbuf[H5C__MAX_EPOCH_MARKERS+1];
int32_t epoch_marker_ringbuf_first;
int32_t epoch_marker_ringbuf_last;
int32_t epoch_marker_ringbuf_size;
H5C_cache_entry_t epoch_markers[H5C__MAX_EPOCH_MARKERS];
int64_t cache_hits;
int64_t cache_accesses;
#if H5C_COLLECT_CACHE_STATS
/* stats fields */
int64_t hits[H5C__MAX_NUM_TYPE_IDS + 1];
int64_t misses[H5C__MAX_NUM_TYPE_IDS + 1];
int64_t insertions[H5C__MAX_NUM_TYPE_IDS + 1];
int64_t clears[H5C__MAX_NUM_TYPE_IDS + 1];
int64_t flushes[H5C__MAX_NUM_TYPE_IDS + 1];
int64_t evictions[H5C__MAX_NUM_TYPE_IDS + 1];
int64_t renames[H5C__MAX_NUM_TYPE_IDS + 1];
int64_t total_ht_insertions;
int64_t total_ht_deletions;
int64_t successful_ht_searches;
int64_t total_successful_ht_search_depth;
int64_t failed_ht_searches;
int64_t total_failed_ht_search_depth;
int32_t max_index_len;
size_t max_index_size;
int32_t max_slist_len;
size_t max_slist_size;
int32_t max_pl_len;
size_t max_pl_size;
#if H5C_COLLECT_CACHE_ENTRY_STATS
int32_t max_accesses[H5C__MAX_NUM_TYPE_IDS + 1];
int32_t min_accesses[H5C__MAX_NUM_TYPE_IDS + 1];
int32_t max_clears[H5C__MAX_NUM_TYPE_IDS + 1];
int32_t max_flushes[H5C__MAX_NUM_TYPE_IDS + 1];
size_t max_size[H5C__MAX_NUM_TYPE_IDS + 1];
#endif /* H5C_COLLECT_CACHE_ENTRY_STATS */
#endif /* H5C_COLLECT_CACHE_STATS */
hbool_t skip_file_checks;
hbool_t skip_dxpl_id_checks;
};
#endif /* _H5Cpkg_H */