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pull/5098/head
Alistair Veitch 9 years ago
parent e28e426af5
commit 532519ac21
1 changed files with 158 additions and 168 deletions
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  1. 326
      src/core/census/log.c

326
src/core/census/log.c
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@ -31,64 +31,62 @@
*
*/
/* Available log space is divided up in blocks of
CENSUS_LOG_2_MAX_RECORD_SIZE bytes. A block can be in one of the
following three data structures:
- Free blocks (free_block_list)
- Blocks with unread data (dirty_block_list)
- Blocks currently attached to cores (core_local_blocks[])
census_log_start_write() moves a block from core_local_blocks[] to the
end of dirty_block_list when block:
- is out-of-space OR
- has an incomplete record (an incomplete record occurs when a thread calls
census_log_start_write() and is context-switched before calling
census_log_end_write()
So, blocks in dirty_block_list are ordered, from oldest to newest, by time
when block is detached from the core.
census_log_read_next() first iterates over dirty_block_list and then
core_local_blocks[]. It moves completely read blocks from dirty_block_list
to free_block_list. Blocks in core_local_blocks[] are not freed, even when
completely read.
If log is configured to discard old records and free_block_list is empty,
census_log_start_write() iterates over dirty_block_list to allocate a
new block. It moves the oldest available block (no pending read/write) to
core_local_blocks[].
core_local_block_struct is used to implement a map from core id to the block
associated with that core. This mapping is advisory. It is possible that the
block returned by this mapping is no longer associated with that core. This
mapping is updated, lazily, by census_log_start_write().
Locking in block struct:
Exclusive g_log.lock must be held before calling any functions operatong on
block structs except census_log_start_write() and
census_log_end_write().
Writes to a block are serialized via writer_lock.
census_log_start_write() acquires this lock and
census_log_end_write() releases it. On failure to acquire the lock,
writer allocates a new block for the current core and updates
core_local_block accordingly.
Simultaneous read and write access is allowed. Readers can safely read up to
committed bytes (bytes_committed).
reader_lock protects the block, currently being read, from getting recycled.
start_read() acquires reader_lock and end_read() releases the lock.
Read/write access to a block is disabled via try_disable_access(). It returns
with both writer_lock and reader_lock held. These locks are subsequently
released by enable_access() to enable access to the block.
A note on naming: Most function/struct names are prepended by cl_
(shorthand for census_log). Further, functions that manipulate structures
include the name of the structure, which will be passed as the first
argument. E.g. cl_block_initialize() will initialize a cl_block.
*/
// Implements an efficient in-memory log, optimized for multiple writers and
// a single reader. Available log space is divided up in blocks of
// CENSUS_LOG_2_MAX_RECORD_SIZE bytes. A block can be in one of the following
// three data structures:
// - Free blocks (free_block_list)
// - Blocks with unread data (dirty_block_list)
// - Blocks currently attached to cores (core_local_blocks[])
//
// census_log_start_write() moves a block from core_local_blocks[] to the end of
// dirty_block_list when block:
// - is out-of-space OR
// - has an incomplete record (an incomplete record occurs when a thread calls
// census_log_start_write() and is context-switched before calling
// census_log_end_write()
// So, blocks in dirty_block_list are ordered, from oldest to newest, by the
// time when block is detached from the core.
//
// census_log_read_next() first iterates over dirty_block_list and then
// core_local_blocks[]. It moves completely read blocks from dirty_block_list
// to free_block_list. Blocks in core_local_blocks[] are not freed, even when
// completely read.
//
// If the log is configured to discard old records and free_block_list is empty,
// census_log_start_write() iterates over dirty_block_list to allocate a
// new block. It moves the oldest available block (no pending read/write) to
// core_local_blocks[].
//
// core_local_block_struct is used to implement a map from core id to the block
// associated with that core. This mapping is advisory. It is possible that the
// block returned by this mapping is no longer associated with that core. This
// mapping is updated, lazily, by census_log_start_write().
//
// Locking in block struct:
//
// Exclusive g_log.lock must be held before calling any functions operating on
// block structs except census_log_start_write() and census_log_end_write().
//
// Writes to a block are serialized via writer_lock. census_log_start_write()
// acquires this lock and census_log_end_write() releases it. On failure to
// acquire the lock, writer allocates a new block for the current core and
// updates core_local_block accordingly.
//
// Simultaneous read and write access is allowed. Readers can safely read up to
// committed bytes (bytes_committed).
//
// reader_lock protects the block, currently being read, from getting recycled.
// start_read() acquires reader_lock and end_read() releases the lock.
//
// Read/write access to a block is disabled via try_disable_access(). It returns
// with both writer_lock and reader_lock held. These locks are subsequently
// released by enable_access() to enable access to the block.
//
// A note on naming: Most function/struct names are prepended by cl_
// (shorthand for census_log). Further, functions that manipulate structures
// include the name of the structure, which will be passed as the first
// argument. E.g. cl_block_initialize() will initialize a cl_block.
#include "src/core/census/log.h"
#include <grpc/support/alloc.h>
@ -100,7 +98,7 @@
#include <stdbool.h>
#include <string.h>
/* End of platform specific code */
// End of platform specific code
typedef struct census_log_block_list_struct {
struct census_log_block_list_struct* next;
@ -109,29 +107,29 @@ typedef struct census_log_block_list_struct {
} cl_block_list_struct;
typedef struct census_log_block {
/* Pointer to underlying buffer */
// Pointer to underlying buffer.
char* buffer;
gpr_atm writer_lock;
gpr_atm reader_lock;
/* Keeps completely written bytes. Declared atomic because accessed
simultaneously by reader and writer. */
// Keeps completely written bytes. Declared atomic because accessed
// simultaneously by reader and writer.
gpr_atm bytes_committed;
/* Bytes already read */
// Bytes already read.
size_t bytes_read;
/* Links for list */
// Links for list.
cl_block_list_struct link;
/* We want this structure to be cacheline aligned. We assume the following
sizes for the various parts on 32/64bit systems:
type 32b size 64b size
char* 4 8
3x gpr_atm 12 24
size_t 4 8
cl_block_list_struct 12 24
TOTAL 32 64
Depending on the size of our cacheline and the architecture, we
selectively add char buffering to this structure. The size is checked
via assert in census_log_initialize(). */
// We want this structure to be cacheline aligned. We assume the following
// sizes for the various parts on 32/64bit systems:
// type 32b size 64b size
// char* 4 8
// 3x gpr_atm 12 24
// size_t 4 8
// cl_block_list_struct 12 24
// TOTAL 32 64
//
// Depending on the size of our cacheline and the architecture, we
// selectively add char buffering to this structure. The size is checked
// via assert in census_log_initialize().
#if defined(GPR_ARCH_64)
#define CL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 64)
#else
@ -146,17 +144,17 @@ typedef struct census_log_block {
#endif
} cl_block;
/* A list of cl_blocks, doubly-linked through cl_block::link. */
// A list of cl_blocks, doubly-linked through cl_block::link.
typedef struct census_log_block_list {
int32_t count; /* Number of items in list. */
cl_block_list_struct ht; /* head/tail of linked list. */
int32_t count; // Number of items in list.
cl_block_list_struct ht; // head/tail of linked list.
} cl_block_list;
/* Cacheline aligned block pointers to avoid false sharing. Block pointer must
be initialized via set_block(), before calling other functions */
// Cacheline aligned block pointers to avoid false sharing. Block pointer must
// be initialized via set_block(), before calling other functions
typedef struct census_log_core_local_block {
gpr_atm block;
/* Ensure cachline alignment: we assume sizeof(gpr_atm) == 4 or 8 */
// Ensure cachline alignment: we assume sizeof(gpr_atm) == 4 or 8
#if defined(GPR_ARCH_64)
#define CL_CORE_LOCAL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 8)
#else
@ -173,40 +171,38 @@ typedef struct census_log_core_local_block {
struct census_log {
int discard_old_records;
/* Number of cores (aka hardware-contexts) */
// Number of cores (aka hardware-contexts)
unsigned num_cores;
/* number of CENSUS_LOG_2_MAX_RECORD_SIZE blocks in log */
// number of CENSUS_LOG_2_MAX_RECORD_SIZE blocks in log
uint32_t num_blocks;
cl_block* blocks; /* Block metadata. */
cl_core_local_block* core_local_blocks; /* Keeps core to block mappings. */
cl_block* blocks; // Block metadata.
cl_core_local_block* core_local_blocks; // Keeps core to block mappings.
gpr_mu lock;
int initialized; /* has log been initialized? */
/* Keeps the state of the reader iterator. A value of 0 indicates that
iterator has reached the end. census_log_init_reader() resets the
value to num_core to restart iteration. */
int initialized; // has log been initialized?
// Keeps the state of the reader iterator. A value of 0 indicates that
// iterator has reached the end. census_log_init_reader() resets the value
// to num_core to restart iteration.
uint32_t read_iterator_state;
/* Points to the block being read. If non-NULL, the block is locked for
reading (block_being_read_->reader_lock is held). */
// Points to the block being read. If non-NULL, the block is locked for
// reading(block_being_read_->reader_lock is held).
cl_block* block_being_read;
/* A non-zero value indicates that log is full. */
gpr_atm is_full;
char* buffer;
cl_block_list free_block_list;
cl_block_list dirty_block_list;
gpr_atm out_of_space_count;
};
/* Single internal log */
// Single internal log.
static struct census_log g_log;
/* Functions that operate on an atomic memory location used as a lock */
// Functions that operate on an atomic memory location used as a lock.
/* Returns non-zero if lock is acquired */
// Returns non-zero if lock is acquired.
static int cl_try_lock(gpr_atm* lock) { return gpr_atm_acq_cas(lock, 0, 1); }
static void cl_unlock(gpr_atm* lock) { gpr_atm_rel_store(lock, 0); }
/* Functions that operate on cl_core_local_block's */
// Functions that operate on cl_core_local_block's.
static void cl_core_local_block_set_block(cl_core_local_block* clb,
cl_block* block) {
@ -217,7 +213,7 @@ static cl_block* cl_core_local_block_get_block(cl_core_local_block* clb) {
return (cl_block*)gpr_atm_acq_load(&clb->block);
}
/* Functions that operate on cl_block_list_struct's */
// Functions that operate on cl_block_list_struct's.
static void cl_block_list_struct_initialize(cl_block_list_struct* bls,
cl_block* block) {
@ -225,19 +221,19 @@ static void cl_block_list_struct_initialize(cl_block_list_struct* bls,
bls->block = block;
}
/* Functions that operate on cl_block_list's */
// Functions that operate on cl_block_list's.
static void cl_block_list_initialize(cl_block_list* list) {
list->count = 0;
cl_block_list_struct_initialize(&list->ht, NULL);
}
/* Returns head of *this, or NULL if empty. */
// Returns head of *this, or NULL if empty.
static cl_block* cl_block_list_head(cl_block_list* list) {
return list->ht.next->block;
}
/* Insert element *e after *pos. */
// Insert element *e after *pos.
static void cl_block_list_insert(cl_block_list* list, cl_block_list_struct* pos,
cl_block_list_struct* e) {
list->count++;
@ -247,24 +243,24 @@ static void cl_block_list_insert(cl_block_list* list, cl_block_list_struct* pos,
e->prev->next = e;
}
/* Insert block at the head of the list */
// Insert block at the head of the list
static void cl_block_list_insert_at_head(cl_block_list* list, cl_block* block) {
cl_block_list_insert(list, &list->ht, &block->link);
}
/* Insert block at the tail of the list */
// Insert block at the tail of the list.
static void cl_block_list_insert_at_tail(cl_block_list* list, cl_block* block) {
cl_block_list_insert(list, list->ht.prev, &block->link);
}
/* Removes block *b. Requires *b be in the list. */
// Removes block *b. Requires *b be in the list.
static void cl_block_list_remove(cl_block_list* list, cl_block* b) {
list->count--;
b->link.next->prev = b->link.prev;
b->link.prev->next = b->link.next;
}
/* Functions that operate on cl_block's */
// Functions that operate on cl_block's
static void cl_block_initialize(cl_block* block, char* buffer) {
block->buffer = buffer;
@ -275,7 +271,7 @@ static void cl_block_initialize(cl_block* block, char* buffer) {
cl_block_list_struct_initialize(&block->link, block);
}
/* Guards against exposing partially written buffer to the reader. */
// Guards against exposing partially written buffer to the reader.
static void cl_block_set_bytes_committed(cl_block* block,
size_t bytes_committed) {
gpr_atm_rel_store(&block->bytes_committed, (gpr_atm)bytes_committed);
@ -285,13 +281,13 @@ static size_t cl_block_get_bytes_committed(cl_block* block) {
return (size_t)gpr_atm_acq_load(&block->bytes_committed);
}
/* Tries to disable future read/write access to this block. Succeeds if:
- no in-progress write AND
- no in-progress read AND
- 'discard_data' set to true OR no unread data
On success, clears the block state and returns with writer_lock_ and
reader_lock_ held. These locks are released by a subsequent
cl_block_access_enable() call. */
// Tries to disable future read/write access to this block. Succeeds if:
// - no in-progress write AND
// - no in-progress read AND
// - 'discard_data' set to true OR no unread data
// On success, clears the block state and returns with writer_lock_ and
// reader_lock_ held. These locks are released by a subsequent
// cl_block_access_enable() call.
static bool cl_block_try_disable_access(cl_block* block, int discard_data) {
if (!cl_try_lock(&block->writer_lock)) {
return false;
@ -316,13 +312,12 @@ static void cl_block_enable_access(cl_block* block) {
cl_unlock(&block->writer_lock);
}
/* Returns with writer_lock held. */
// Returns with writer_lock held.
static void* cl_block_start_write(cl_block* block, size_t size) {
size_t bytes_committed;
if (!cl_try_lock(&block->writer_lock)) {
return NULL;
}
bytes_committed = cl_block_get_bytes_committed(block);
size_t bytes_committed = cl_block_get_bytes_committed(block);
if (bytes_committed + size > CENSUS_LOG_MAX_RECORD_SIZE) {
cl_unlock(&block->writer_lock);
return NULL;
@ -330,26 +325,26 @@ static void* cl_block_start_write(cl_block* block, size_t size) {
return block->buffer + bytes_committed;
}
/* Releases writer_lock and increments committed bytes by 'bytes_written'.
'bytes_written' must be <= 'size' specified in the corresponding
StartWrite() call. This function is thread-safe. */
// Releases writer_lock and increments committed bytes by 'bytes_written'.
// 'bytes_written' must be <= 'size' specified in the corresponding
// StartWrite() call. This function is thread-safe.
static void cl_block_end_write(cl_block* block, size_t bytes_written) {
cl_block_set_bytes_committed(
block, cl_block_get_bytes_committed(block) + bytes_written);
cl_unlock(&block->writer_lock);
}
/* Returns a pointer to the first unread byte in buffer. The number of bytes
available are returned in 'bytes_available'. Acquires reader lock that is
released by a subsequent cl_block_end_read() call. Returns NULL if:
- read in progress
- no data available */
// Returns a pointer to the first unread byte in buffer. The number of bytes
// available are returned in 'bytes_available'. Acquires reader lock that is
// released by a subsequent cl_block_end_read() call. Returns NULL if:
// - read in progress
// - no data available
static void* cl_block_start_read(cl_block* block, size_t* bytes_available) {
if (!cl_try_lock(&block->reader_lock)) {
return NULL;
}
/* bytes_committed may change from under us. Use bytes_available to update
bytes_read below. */
// bytes_committed may change from under us. Use bytes_available to update
// bytes_read below.
size_t bytes_committed = cl_block_get_bytes_committed(block);
GPR_ASSERT(bytes_committed >= block->bytes_read);
*bytes_available = bytes_committed - block->bytes_read;
@ -366,10 +361,10 @@ static void cl_block_end_read(cl_block* block) {
cl_unlock(&block->reader_lock);
}
/* Internal functions operating on g_log */
// Internal functions operating on g_log
/* Allocates a new free block (or recycles an available dirty block if log is
configured to discard old records). Returns NULL if out-of-space. */
// Allocates a new free block (or recycles an available dirty block if log is
// configured to discard old records). Returns NULL if out-of-space.
static cl_block* cl_allocate_block(void) {
cl_block* block = cl_block_list_head(&g_log.free_block_list);
if (block != NULL) {
@ -377,10 +372,10 @@ static cl_block* cl_allocate_block(void) {
return block;
}
if (!g_log.discard_old_records) {
/* No free block and log is configured to keep old records. */
// No free block and log is configured to keep old records.
return NULL;
}
/* Recycle dirty block. Start from the oldest. */
// Recycle dirty block. Start from the oldest.
for (block = cl_block_list_head(&g_log.dirty_block_list); block != NULL;
block = block->link.next->block) {
if (cl_block_try_disable_access(block, 1 /* discard data */)) {
@ -391,15 +386,15 @@ static cl_block* cl_allocate_block(void) {
return NULL;
}
/* Allocates a new block and updates core id => block mapping. 'old_block'
points to the block that the caller thinks is attached to
'core_id'. 'old_block' may be NULL. Returns true if:
- allocated a new block OR
- 'core_id' => 'old_block' mapping changed (another thread allocated a
block before lock was acquired). */
// Allocates a new block and updates core id => block mapping. 'old_block'
// points to the block that the caller thinks is attached to
// 'core_id'. 'old_block' may be NULL. Returns true if:
// - allocated a new block OR
// - 'core_id' => 'old_block' mapping changed (another thread allocated a
// block before lock was acquired).
static bool cl_allocate_core_local_block(uint32_t core_id,
cl_block* old_block) {
/* Now that we have the lock, check if core-local mapping has changed. */
// Now that we have the lock, check if core-local mapping has changed.
cl_core_local_block* core_local_block = &g_log.core_local_blocks[core_id];
cl_block* block = cl_core_local_block_get_block(core_local_block);
if ((block != NULL) && (block != old_block)) {
@ -411,7 +406,6 @@ static bool cl_allocate_core_local_block(uint32_t core_id,
}
block = cl_allocate_block();
if (block == NULL) {
gpr_atm_rel_store(&g_log.is_full, 1);
return false;
}
cl_core_local_block_set_block(core_local_block, block);
@ -425,21 +419,22 @@ static cl_block* cl_get_block(void* record) {
return &g_log.blocks[index];
}
/* Gets the next block to read and tries to free 'prev' block (if not NULL).
Returns NULL if reached the end. */
// Gets the next block to read and tries to free 'prev' block (if not NULL).
// Returns NULL if reached the end.
static cl_block* cl_next_block_to_read(cl_block* prev) {
cl_block* block = NULL;
if (g_log.read_iterator_state == g_log.num_cores) {
/* We are traversing dirty list; find the next dirty block. */
// We are traversing dirty list; find the next dirty block.
if (prev != NULL) {
/* Try to free the previous block if there is no unread data. This block
may have unread data if previously incomplete record completed between
read_next() calls. */
// Try to free the previous block if there is no unread data. This
// block
// may have unread data if previously incomplete record completed
// between
// read_next() calls.
block = prev->link.next->block;
if (cl_block_try_disable_access(prev, 0 /* do not discard data */)) {
cl_block_list_remove(&g_log.dirty_block_list, prev);
cl_block_list_insert_at_head(&g_log.free_block_list, prev);
gpr_atm_rel_store(&g_log.is_full, 0);
}
} else {
block = cl_block_list_head(&g_log.dirty_block_list);
@ -447,7 +442,7 @@ static cl_block* cl_next_block_to_read(cl_block* prev) {
if (block != NULL) {
return block;
}
/* We are done with the dirty list; moving on to core-local blocks. */
// We are done with the dirty list; moving on to core-local blocks.
}
while (g_log.read_iterator_state > 0) {
g_log.read_iterator_state--;
@ -460,27 +455,26 @@ static cl_block* cl_next_block_to_read(cl_block* prev) {
return NULL;
}
#define CL_LOG_2_MB 20 /* 2^20 = 1MB */
#define CL_LOG_2_MB 20 // 2^20 = 1MB
/* External functions: primary stats_log interface */
// External functions: primary stats_log interface
void census_log_initialize(size_t size_in_mb, int discard_old_records) {
/* Check cacheline alignment. */
// Check cacheline alignment.
GPR_ASSERT(sizeof(cl_block) % GPR_CACHELINE_SIZE == 0);
GPR_ASSERT(sizeof(cl_core_local_block) % GPR_CACHELINE_SIZE == 0);
GPR_ASSERT(!g_log.initialized);
g_log.discard_old_records = discard_old_records;
g_log.num_cores = gpr_cpu_num_cores();
/* Ensure that we will not get any overflow in calaculating num_blocks */
// Ensure that we will not get any overflow in calaculating num_blocks
GPR_ASSERT(CL_LOG_2_MB >= CENSUS_LOG_2_MAX_RECORD_SIZE);
GPR_ASSERT(size_in_mb < 1000);
/* Ensure at least as many blocks as there are cores. */
// Ensure at least 2x as many blocks as there are cores.
g_log.num_blocks =
(uint32_t)GPR_MAX(g_log.num_cores, (size_in_mb << CL_LOG_2_MB) >>
CENSUS_LOG_2_MAX_RECORD_SIZE);
(uint32_t)GPR_MAX(2 * g_log.num_cores, (size_in_mb << CL_LOG_2_MB) >>
CENSUS_LOG_2_MAX_RECORD_SIZE);
gpr_mu_init(&g_log.lock);
g_log.read_iterator_state = 0;
g_log.block_being_read = NULL;
gpr_atm_rel_store(&g_log.is_full, 0);
g_log.core_local_blocks = (cl_core_local_block*)gpr_malloc_aligned(
g_log.num_cores * sizeof(cl_core_local_block), GPR_CACHELINE_SIZE_LOG);
memset(g_log.core_local_blocks, 0,
@ -515,7 +509,7 @@ void census_log_shutdown(void) {
}
void* census_log_start_write(size_t size) {
/* Used to bound number of times block allocation is attempted. */
// Used to bound number of times block allocation is attempted.
GPR_ASSERT(size > 0);
GPR_ASSERT(g_log.initialized);
if (size > CENSUS_LOG_MAX_RECORD_SIZE) {
@ -530,14 +524,10 @@ void* census_log_start_write(size_t size) {
if (block && (record = cl_block_start_write(block, size))) {
return record;
}
/* Need to allocate a new block. We are here if:
- No block associated with the core OR
- Write in-progress on the block OR
- block is out of space */
if (gpr_atm_acq_load(&g_log.is_full)) {
gpr_atm_no_barrier_fetch_add(&g_log.out_of_space_count, 1);
return NULL;
}
// Need to allocate a new block. We are here if:
// - No block associated with the core OR
// - Write in-progress on the block OR
// - block is out of space
gpr_mu_lock(&g_log.lock);
bool allocated = cl_allocate_core_local_block(core_id, block);
gpr_mu_unlock(&g_log.lock);
@ -546,7 +536,7 @@ void* census_log_start_write(size_t size) {
return NULL;
}
} while (attempts_remaining--);
/* Give up. */
// Give up.
gpr_atm_no_barrier_fetch_add(&g_log.out_of_space_count, 1);
return NULL;
}
@ -559,7 +549,7 @@ void census_log_end_write(void* record, size_t bytes_written) {
void census_log_init_reader(void) {
GPR_ASSERT(g_log.initialized);
gpr_mu_lock(&g_log.lock);
/* If a block is locked for reading unlock it. */
// If a block is locked for reading unlock it.
if (g_log.block_being_read != NULL) {
cl_block_end_read(g_log.block_being_read);
g_log.block_being_read = NULL;
@ -594,7 +584,7 @@ size_t census_log_remaining_space(void) {
size_t space = 0;
gpr_mu_lock(&g_log.lock);
if (g_log.discard_old_records) {
/* Remaining space is not meaningful; just return the entire log space. */
// Remaining space is not meaningful; just return the entire log space.
space = g_log.num_blocks << CENSUS_LOG_2_MAX_RECORD_SIZE;
} else {
GPR_ASSERT(g_log.free_block_list.count >= 0);

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