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SHMEM_LOCKS: MCS implementation of SHMEM LOCKS Adding MCS algorithm-based implementation for shmem_locks to improve performance for large scale SHMEM applications using locks. MCS lock is now the default algorithm, use the following MCA parameter to disable. --mca oshmem_enable_mcs_lock 0 to disable mcs locks and revert to default ticket locking. --mca oshmem_api_verbose 10 for debug information on shmem_locks. Signed-off-by: Vishwanath Venkatesan <[email protected]>
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Vishwanath Venkatesan
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Oct 18, 2023
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| Original file line number | Diff line number | Diff line change |
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| /* | ||
| * Copyright (c) 2023 NVIDIA Corporation. | ||
| * All rights reserved. | ||
| * | ||
| * $COPYRIGHT$ | ||
| * | ||
| * Additional copyrights may follow | ||
| * | ||
| * $HEADER$ | ||
| */ | ||
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| #include "oshmem_config.h" | ||
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| #include "oshmem/constants.h" | ||
| #include "oshmem/include/shmem.h" | ||
| #include "oshmem/runtime/params.h" | ||
| #include "oshmem/runtime/runtime.h" | ||
| #include <stdlib.h> | ||
| #include <memory.h> | ||
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| #include "oshmem/shmem/shmem_api_logger.h" | ||
| #include "oshmem/shmem/shmem_lock.h" | ||
| #include "oshmem/mca/memheap/memheap.h" | ||
| #include "oshmem/mca/memheap/base/base.h" | ||
| #include "oshmem/mca/atomic/atomic.h" | ||
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| #define OPAL_BITWISE_SIZEOF_LONG (SIZEOF_LONG * 8) | ||
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| /** Use basic MCS distributed lock algorithm for lock */ | ||
| struct shmem_mcs_lock { | ||
| /** has meaning only on MCSQ_TAIL OWNER */ | ||
| int tail; | ||
| /** It has meaning on all PEs */ | ||
| /** The next pointer is a combination of the PE ID and wait signal */ | ||
| int next; | ||
| }; | ||
| typedef struct shmem_mcs_lock shmem_mcs_lock_t; | ||
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| #define SHMEM_MCSL_TAIL_OWNER(lock_ptr)\ | ||
| (((uintptr_t)(lock_ptr) / sizeof(long)) % shmem_n_pes()) | ||
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| #define SHMEM_MCSL_NEXT_MASK 0x7FFFFFFFU | ||
| #define SHMEM_MCSL_SIGNAL_MASK 0x80000000U /** Wait signal mask */ | ||
| #define SHMEM_MCSL_NEXT(lock_val) ((lock_val) & SHMEM_MCSL_NEXT_MASK) | ||
| /** Improve readability */ | ||
| #define SHMEM_MCSL_GET_PE(tail_val) ((tail_val) & SHMEM_MCSL_NEXT_MASK) | ||
| #define SHMEM_MCSL_SIGNAL(lock_val) ((lock_val) & SHMEM_MCSL_SIGNAL_MASK) | ||
| #define SHMEM_MCSL_SET_SIGNAL(lock_val) ((lock_val) | SHMEM_MCSL_SIGNAL_MASK) | ||
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| void | ||
| _shmem_mcs_set_lock(long *lockp) | ||
| { | ||
| shmem_mcs_lock_t *lock = (shmem_mcs_lock_t *) lockp; | ||
| int mcs_tail_owner = SHMEM_MCSL_TAIL_OWNER(lock); | ||
| int new_tail_req = 0; | ||
| int *tail = &(lock->tail); | ||
| int *next = &(lock->next); | ||
| int my_pe = shmem_my_pe(); | ||
| int curr = 0; | ||
| int out_value = 0; | ||
| int prev_tail = 0; | ||
| int prev_tailpe = 0; | ||
| int tval = 0; | ||
| int tmp_val = 0; | ||
| int retv = 0; | ||
| uint64_t value_tmp = 0; | ||
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| RUNTIME_CHECK_INIT(); | ||
| /** | ||
| * Initializing next pointer to next mask | ||
| * Done atomically to avoid races as NEXT pointer | ||
| * can be modified by other PEs while acquiring or | ||
| * releasing it. | ||
| */ | ||
| /** | ||
| * Can make this to be shmem_atomic_set to be safe | ||
| * in non-cc architectures | ||
| * has an impact on performance | ||
| */ | ||
| value_tmp = SHMEM_MCSL_NEXT_MASK; | ||
| out_value = SHMEM_MCSL_NEXT_MASK; | ||
| retv = MCA_ATOMIC_CALL(swap(oshmem_ctx_default, (void*)next, | ||
| (void*)&out_value, value_tmp, | ||
| sizeof(int), my_pe)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| MCA_SPML_CALL(quiet(oshmem_ctx_default)); | ||
|
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| /** Signal for setting lock */ | ||
| new_tail_req = SHMEM_MCSL_SET_SIGNAL(my_pe); | ||
| /** | ||
| * Swap and make me the new tail and update in tail owner | ||
| * Get the previous tail PE. | ||
| */ | ||
| retv = MCA_ATOMIC_CALL(swap(oshmem_ctx_default, (void *)tail, | ||
| (void*)&prev_tail, | ||
| OSHMEM_ATOMIC_PTR_2_INT(&new_tail_req, | ||
| sizeof(new_tail_req)), | ||
| sizeof(int), mcs_tail_owner)); | ||
| RUNTIME_CHECK_RC(retv); | ||
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| prev_tailpe = SHMEM_MCSL_GET_PE(prev_tail); | ||
| if (SHMEM_MCSL_SIGNAL(prev_tail)) { | ||
| /** | ||
| * Someone else has got the lock before this PE | ||
| * Adding this PE to the previous tail PE's Next pointer | ||
| * Substract the SIGNAL Bit to avoid changing it. | ||
| */ | ||
| tmp_val = my_pe - SHMEM_MCSL_NEXT_MASK; | ||
| retv = MCA_ATOMIC_CALL(add(oshmem_ctx_default, (void*)next, tmp_val, | ||
| sizeof(int), prev_tailpe)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| /** | ||
| * This value to be changed eventually by predecessor | ||
| * when its lock is released. | ||
| * Need to be done atomically to avoid any races where | ||
| * next pointer is modified by another PE acquiring or | ||
| * releasing this. | ||
| */ | ||
| retv = MCA_ATOMIC_CALL(add(oshmem_ctx_default, (void *)next, | ||
| SHMEM_MCSL_SIGNAL_MASK, sizeof(int), | ||
| my_pe)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| MCA_SPML_CALL(quiet(oshmem_ctx_default)); | ||
| /** Wait for predecessor release lock to this PE signal to false. */ | ||
| retv = MCA_ATOMIC_CALL(fadd(oshmem_ctx_default, (void*)next, | ||
| (void*)&curr, tval, sizeof(int), my_pe)); | ||
| RUNTIME_CHECK_RC(retv); | ||
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| while (SHMEM_MCSL_SIGNAL(curr)) { | ||
| retv = MCA_SPML_CALL(wait((void*)next, SHMEM_CMP_NE, | ||
| (void*)&curr, SHMEM_INT)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| retv = MCA_ATOMIC_CALL(fadd(oshmem_ctx_default, (void*)next, | ||
| (void*)&curr, tval, sizeof(int), | ||
| my_pe)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| } | ||
| } | ||
| /** else.. this pe has got the lock as no one else had it */ | ||
| } | ||
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| void | ||
| _shmem_mcs_clear_lock(long *lockp) | ||
| { | ||
| shmem_mcs_lock_t *lock = (shmem_mcs_lock_t *) lockp; | ||
| int mcs_tail_owner = SHMEM_MCSL_TAIL_OWNER(lock); | ||
| int *tail = &(lock->tail); | ||
| int *next = &(lock->next); | ||
| int my_pe = shmem_my_pe(); | ||
| int next_value = 0; | ||
| int swap_cond = 0; | ||
| int prev_value = 0; | ||
| int tval = 0; | ||
| int val_tmp = 0; | ||
| int nmask = 0; | ||
| int a_val = 0; | ||
| int retv = 0; | ||
|
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||
| /** | ||
| * Can make atomic fetch to be safe in non-cc architectures | ||
| * Has impact on performance | ||
| */ | ||
| retv = MCA_ATOMIC_CALL(fadd(oshmem_ctx_default, (void*)next, | ||
| (void*)&next_value, tval, sizeof(int), | ||
| my_pe)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| MCA_SPML_CALL(quiet(oshmem_ctx_default)); | ||
|
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| if (next_value == SHMEM_MCSL_NEXT_MASK) { | ||
| swap_cond = SHMEM_MCSL_SET_SIGNAL(my_pe); | ||
| retv = MCA_ATOMIC_CALL(cswap(oshmem_ctx_default, | ||
| (void *)tail, (uint64_t *)&(prev_value), | ||
| OSHMEM_ATOMIC_PTR_2_INT(&swap_cond, | ||
| sizeof(swap_cond)), | ||
| OSHMEM_ATOMIC_PTR_2_INT(&val_tmp, | ||
| sizeof(val_tmp)), sizeof(int), | ||
| mcs_tail_owner)); | ||
| RUNTIME_CHECK_RC(retv); | ||
|
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||
| /** I am the tail.. and lock is released */ | ||
| if (prev_value == swap_cond) { | ||
| return; | ||
| } | ||
| /** | ||
| * I am not the tail, another PE maybe racing to acquire lock, | ||
| * let them complete setting themselves as our next | ||
| */ | ||
| nmask = SHMEM_MCSL_NEXT_MASK; | ||
| while(next_value == nmask) { | ||
| retv = MCA_SPML_CALL(wait((void*)next, SHMEM_CMP_NE, | ||
| (void*)&nmask, SHMEM_INT)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| retv = MCA_ATOMIC_CALL(fadd(oshmem_ctx_default, (void*)next, | ||
| (void*)&next_value, tval, | ||
| sizeof(int), my_pe)); | ||
| RUNTIME_CHECK_RC(retv); | ||
| } | ||
| } | ||
| /** There is a successor release lock to the successor */ | ||
| a_val = SHMEM_MCSL_SIGNAL_MASK; | ||
| retv = MCA_ATOMIC_CALL(add(oshmem_ctx_default, | ||
| (void *)next, a_val, sizeof(a_val), | ||
| SHMEM_MCSL_NEXT(next_value))); | ||
| RUNTIME_CHECK_RC(retv); | ||
| MCA_SPML_CALL(quiet(oshmem_ctx_default)); | ||
| } | ||
|
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| int | ||
| _shmem_mcs_test_lock(long *lockp) | ||
| { | ||
| shmem_mcs_lock_t *lock = (shmem_mcs_lock_t *) lockp; | ||
| int mcs_tail_owner = SHMEM_MCSL_TAIL_OWNER(lock); | ||
| int new_tail_req = 0; | ||
| int prev_tail = 0; | ||
| int tmp_cond = 0; | ||
| int *tail = &(lock->tail); | ||
| int *next = &(lock->next); | ||
| int my_pe = shmem_my_pe(); | ||
| int retv = 0; | ||
|
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| /** Initializing next pointer to next mask */ | ||
| *next = SHMEM_MCSL_NEXT_MASK; | ||
|
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| /** Signal for setting lock */ | ||
| new_tail_req = SHMEM_MCSL_SET_SIGNAL(my_pe); | ||
|
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| /** Check if previously cleared before swapping */ | ||
| retv = MCA_ATOMIC_CALL(cswap(oshmem_ctx_default, | ||
| (void *)tail, (uint64_t *)&(prev_tail), | ||
| OSHMEM_ATOMIC_PTR_2_INT(&tmp_cond, | ||
| sizeof(tmp_cond)), | ||
| OSHMEM_ATOMIC_PTR_2_INT(&new_tail_req, | ||
| sizeof(new_tail_req)), | ||
| sizeof(int), mcs_tail_owner)); | ||
| RUNTIME_CHECK_RC(retv); | ||
|
|
||
| return (0 != prev_tail); | ||
| } |
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