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Diffstat (limited to 'src/core/ext/census/mlog.c')
| -rw-r--r-- | src/core/ext/census/mlog.c | 600 |
1 files changed, 600 insertions, 0 deletions
diff --git a/src/core/ext/census/mlog.c b/src/core/ext/census/mlog.c new file mode 100644 index 0000000000..698b7096ab --- /dev/null +++ b/src/core/ext/census/mlog.c @@ -0,0 +1,600 @@ +/* + * + * Copyright 2015, Google Inc. + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions are + * met: + * + * * Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * * Redistributions in binary form must reproduce the above + * copyright notice, this list of conditions and the following disclaimer + * in the documentation and/or other materials provided with the + * distribution. + * * Neither the name of Google Inc. nor the names of its + * contributors may be used to endorse or promote products derived from + * this software without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR + * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT + * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, + * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT + * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, + * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY + * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT + * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE + * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + * + */ + +// 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/ext/census/mlog.h" +#include <grpc/support/alloc.h> +#include <grpc/support/atm.h> +#include <grpc/support/cpu.h> +#include <grpc/support/log.h> +#include <grpc/support/sync.h> +#include <grpc/support/useful.h> +#include <stdbool.h> +#include <string.h> + +// End of platform specific code + +typedef struct census_log_block_list_struct { + struct census_log_block_list_struct* next; + struct census_log_block_list_struct* prev; + struct census_log_block* block; +} cl_block_list_struct; + +typedef struct census_log_block { + // 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. + gpr_atm bytes_committed; + // Bytes already read. + size_t bytes_read; + // 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(). +#if defined(GPR_ARCH_64) +#define CL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 64) +#else +#if defined(GPR_ARCH_32) +#define CL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 32) +#else +#error "Unknown architecture" +#endif +#endif +#if CL_BLOCK_PAD_SIZE > 0 + char padding[CL_BLOCK_PAD_SIZE]; +#endif +} cl_block; + +// 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. +} cl_block_list; + +// 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 +#if defined(GPR_ARCH_64) +#define CL_CORE_LOCAL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 8) +#else +#if defined(GPR_ARCH_32) +#define CL_CORE_LOCAL_BLOCK_PAD_SIZE (GPR_CACHELINE_SIZE - 4) +#else +#error "Unknown architecture" +#endif +#endif +#if CL_CORE_LOCAL_BLOCK_PAD_SIZE > 0 + char padding[CL_CORE_LOCAL_BLOCK_PAD_SIZE]; +#endif +} cl_core_local_block; + +struct census_log { + int discard_old_records; + // Number of cores (aka hardware-contexts) + unsigned num_cores; + // 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. + 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. + 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). + cl_block* block_being_read; + char* buffer; + cl_block_list free_block_list; + cl_block_list dirty_block_list; + gpr_atm out_of_space_count; +}; + +// Single internal log. +static struct census_log g_log; + +// Functions that operate on an atomic memory location used as a lock. + +// 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. + +static void cl_core_local_block_set_block(cl_core_local_block* clb, + cl_block* block) { + gpr_atm_rel_store(&clb->block, (gpr_atm)block); +} + +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. + +static void cl_block_list_struct_initialize(cl_block_list_struct* bls, + cl_block* block) { + bls->next = bls->prev = bls; + bls->block = block; +} + +// 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. +static cl_block* cl_block_list_head(cl_block_list* list) { + return list->ht.next->block; +} + +// 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++; + e->next = pos->next; + e->prev = pos; + e->next->prev = e; + e->prev->next = e; +} + +// 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. +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. +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 + +static void cl_block_initialize(cl_block* block, char* buffer) { + block->buffer = buffer; + gpr_atm_rel_store(&block->writer_lock, 0); + gpr_atm_rel_store(&block->reader_lock, 0); + gpr_atm_rel_store(&block->bytes_committed, 0); + block->bytes_read = 0; + cl_block_list_struct_initialize(&block->link, block); +} + +// 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); +} + +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. +static bool cl_block_try_disable_access(cl_block* block, int discard_data) { + if (!cl_try_lock(&block->writer_lock)) { + return false; + } + if (!cl_try_lock(&block->reader_lock)) { + cl_unlock(&block->writer_lock); + return false; + } + if (!discard_data && + (block->bytes_read != cl_block_get_bytes_committed(block))) { + cl_unlock(&block->reader_lock); + cl_unlock(&block->writer_lock); + return false; + } + cl_block_set_bytes_committed(block, 0); + block->bytes_read = 0; + return true; +} + +static void cl_block_enable_access(cl_block* block) { + cl_unlock(&block->reader_lock); + cl_unlock(&block->writer_lock); +} + +// Returns with writer_lock held. +static void* cl_block_start_write(cl_block* block, size_t size) { + if (!cl_try_lock(&block->writer_lock)) { + return NULL; + } + 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; + } + 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. +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 +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. + size_t bytes_committed = cl_block_get_bytes_committed(block); + GPR_ASSERT(bytes_committed >= block->bytes_read); + *bytes_available = bytes_committed - block->bytes_read; + if (*bytes_available == 0) { + cl_unlock(&block->reader_lock); + return NULL; + } + void* record = block->buffer + block->bytes_read; + block->bytes_read += *bytes_available; + return record; +} + +static void cl_block_end_read(cl_block* block) { + cl_unlock(&block->reader_lock); +} + +// 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. +static cl_block* cl_allocate_block(void) { + cl_block* block = cl_block_list_head(&g_log.free_block_list); + if (block != NULL) { + cl_block_list_remove(&g_log.free_block_list, block); + return block; + } + if (!g_log.discard_old_records) { + // No free block and log is configured to keep old records. + return NULL; + } + // 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 */)) { + cl_block_list_remove(&g_log.dirty_block_list, block); + return block; + } + } + 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). +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. + 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)) { + return true; + } + if (block != NULL) { + cl_core_local_block_set_block(core_local_block, NULL); + cl_block_list_insert_at_tail(&g_log.dirty_block_list, block); + } + block = cl_allocate_block(); + if (block == NULL) { + return false; + } + cl_core_local_block_set_block(core_local_block, block); + cl_block_enable_access(block); + return true; +} + +static cl_block* cl_get_block(void* record) { + uintptr_t p = (uintptr_t)((char*)record - g_log.buffer); + uintptr_t index = p >> CENSUS_LOG_2_MAX_RECORD_SIZE; + 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. +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. + 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. + 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); + } + } else { + block = cl_block_list_head(&g_log.dirty_block_list); + } + if (block != NULL) { + return block; + } + // 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--; + block = cl_core_local_block_get_block( + &g_log.core_local_blocks[g_log.read_iterator_state]); + if (block != NULL) { + return block; + } + } + return NULL; +} + +#define CL_LOG_2_MB 20 // 2^20 = 1MB + +// External functions: primary stats_log interface +void census_log_initialize(size_t size_in_mb, int discard_old_records) { + // 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 + GPR_ASSERT(CL_LOG_2_MB >= CENSUS_LOG_2_MAX_RECORD_SIZE); + GPR_ASSERT(size_in_mb < 1000); + // Ensure at least 2x as many blocks as there are cores. + g_log.num_blocks = + (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; + 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, + g_log.num_cores * sizeof(cl_core_local_block)); + g_log.blocks = (cl_block*)gpr_malloc_aligned( + g_log.num_blocks * sizeof(cl_block), GPR_CACHELINE_SIZE_LOG); + memset(g_log.blocks, 0, g_log.num_blocks * sizeof(cl_block)); + g_log.buffer = gpr_malloc(g_log.num_blocks * CENSUS_LOG_MAX_RECORD_SIZE); + memset(g_log.buffer, 0, g_log.num_blocks * CENSUS_LOG_MAX_RECORD_SIZE); + cl_block_list_initialize(&g_log.free_block_list); + cl_block_list_initialize(&g_log.dirty_block_list); + for (uint32_t i = 0; i < g_log.num_blocks; ++i) { + cl_block* block = g_log.blocks + i; + cl_block_initialize(block, g_log.buffer + (CENSUS_LOG_MAX_RECORD_SIZE * i)); + cl_block_try_disable_access(block, 1 /* discard data */); + cl_block_list_insert_at_tail(&g_log.free_block_list, block); + } + gpr_atm_rel_store(&g_log.out_of_space_count, 0); + g_log.initialized = 1; +} + +void census_log_shutdown(void) { + GPR_ASSERT(g_log.initialized); + gpr_mu_destroy(&g_log.lock); + gpr_free_aligned(g_log.core_local_blocks); + g_log.core_local_blocks = NULL; + gpr_free_aligned(g_log.blocks); + g_log.blocks = NULL; + gpr_free(g_log.buffer); + g_log.buffer = NULL; + g_log.initialized = 0; +} + +void* census_log_start_write(size_t size) { + // 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) { + return NULL; + } + uint32_t attempts_remaining = g_log.num_blocks; + uint32_t core_id = gpr_cpu_current_cpu(); + do { + void* record = NULL; + cl_block* block = + cl_core_local_block_get_block(&g_log.core_local_blocks[core_id]); + 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 + gpr_mu_lock(&g_log.lock); + bool allocated = cl_allocate_core_local_block(core_id, block); + gpr_mu_unlock(&g_log.lock); + if (!allocated) { + gpr_atm_no_barrier_fetch_add(&g_log.out_of_space_count, 1); + return NULL; + } + } while (attempts_remaining--); + // Give up. + gpr_atm_no_barrier_fetch_add(&g_log.out_of_space_count, 1); + return NULL; +} + +void census_log_end_write(void* record, size_t bytes_written) { + GPR_ASSERT(g_log.initialized); + cl_block_end_write(cl_get_block(record), 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 (g_log.block_being_read != NULL) { + cl_block_end_read(g_log.block_being_read); + g_log.block_being_read = NULL; + } + g_log.read_iterator_state = g_log.num_cores; + gpr_mu_unlock(&g_log.lock); +} + +const void* census_log_read_next(size_t* bytes_available) { + GPR_ASSERT(g_log.initialized); + gpr_mu_lock(&g_log.lock); + if (g_log.block_being_read != NULL) { + cl_block_end_read(g_log.block_being_read); + } + do { + g_log.block_being_read = cl_next_block_to_read(g_log.block_being_read); + if (g_log.block_being_read != NULL) { + void* record = + cl_block_start_read(g_log.block_being_read, bytes_available); + if (record != NULL) { + gpr_mu_unlock(&g_log.lock); + return record; + } + } + } while (g_log.block_being_read != NULL); + gpr_mu_unlock(&g_log.lock); + return NULL; +} + +size_t census_log_remaining_space(void) { + GPR_ASSERT(g_log.initialized); + 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. + space = g_log.num_blocks << CENSUS_LOG_2_MAX_RECORD_SIZE; + } else { + GPR_ASSERT(g_log.free_block_list.count >= 0); + space = (size_t)g_log.free_block_list.count * CENSUS_LOG_MAX_RECORD_SIZE; + } + gpr_mu_unlock(&g_log.lock); + return space; +} + +int64_t census_log_out_of_space_count(void) { + GPR_ASSERT(g_log.initialized); + return gpr_atm_acq_load(&g_log.out_of_space_count); +} |