rte_rcu_qsbr.h

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/* SPDX-License-Identifier: BSD-3-Clause
 * Copyright (c) 2018 Arm Limited
 */

#ifndef _RTE_RCU_QSBR_H_
#define _RTE_RCU_QSBR_H_

#ifdef __cplusplus
extern "C" {
#endif

#include <stdbool.h>
#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
#include <errno.h>
#include <rte_common.h>
#include <rte_memory.h>
#include <rte_lcore.h>
#include <rte_debug.h>
#include <rte_atomic.h>

extern int rte_rcu_log_type;

#if RTE_LOG_DP_LEVEL >= RTE_LOG_DEBUG
#define __RTE_RCU_DP_LOG(level, fmt, args...) \
    rte_log(RTE_LOG_ ## level, rte_rcu_log_type, \
        "%s(): " fmt "\n", __func__, ## args)
#else
#define __RTE_RCU_DP_LOG(level, fmt, args...)
#endif

#if defined(RTE_LIBRTE_RCU_DEBUG)
#define __RTE_RCU_IS_LOCK_CNT_ZERO(v, thread_id, level, fmt, args...) do {\
    if (v->qsbr_cnt[thread_id].lock_cnt) \
        rte_log(RTE_LOG_ ## level, rte_rcu_log_type, \
            "%s(): " fmt "\n", __func__, ## args); \
} while (0)
#else
#define __RTE_RCU_IS_LOCK_CNT_ZERO(v, thread_id, level, fmt, args...)
#endif

/* Registered thread IDs are stored as a bitmap of 64b element array.
 * Given thread id needs to be converted to index into the array and
 * the id within the array element.
 */
#define __RTE_QSBR_THRID_ARRAY_ELM_SIZE (sizeof(uint64_t) * 8)
#define __RTE_QSBR_THRID_ARRAY_SIZE(max_threads) \
    RTE_ALIGN(RTE_ALIGN_MUL_CEIL(max_threads, \
        __RTE_QSBR_THRID_ARRAY_ELM_SIZE) >> 3, RTE_CACHE_LINE_SIZE)
#define __RTE_QSBR_THRID_ARRAY_ELM(v, i) ((uint64_t *) \
    ((struct rte_rcu_qsbr_cnt *)(v + 1) + v->max_threads) + i)
#define __RTE_QSBR_THRID_INDEX_SHIFT 6
#define __RTE_QSBR_THRID_MASK 0x3f
#define RTE_QSBR_THRID_INVALID 0xffffffff

/* Worker thread counter */
struct rte_rcu_qsbr_cnt {
    uint64_t cnt;
    uint32_t lock_cnt;
} __rte_cache_aligned;

#define __RTE_QSBR_CNT_THR_OFFLINE 0
#define __RTE_QSBR_CNT_INIT 1
#define __RTE_QSBR_CNT_MAX ((uint64_t)~0)

/* RTE Quiescent State variable structure.
 * This structure has two elements that vary in size based on the
 * 'max_threads' parameter.
 * 1) Quiescent state counter array
 * 2) Register thread ID array
 */
struct rte_rcu_qsbr {
    uint64_t token __rte_cache_aligned;
    uint64_t acked_token;
    uint32_t num_elems __rte_cache_aligned;
    uint32_t num_threads;
    uint32_t max_threads;
    struct rte_rcu_qsbr_cnt qsbr_cnt[0] __rte_cache_aligned;
} __rte_cache_aligned;

__rte_experimental
size_t
rte_rcu_qsbr_get_memsize(uint32_t max_threads);

__rte_experimental
int
rte_rcu_qsbr_init(struct rte_rcu_qsbr *v, uint32_t max_threads);

__rte_experimental
int
rte_rcu_qsbr_thread_register(struct rte_rcu_qsbr *v, unsigned int thread_id);

__rte_experimental
int
rte_rcu_qsbr_thread_unregister(struct rte_rcu_qsbr *v, unsigned int thread_id);

__rte_experimental
static __rte_always_inline void
rte_rcu_qsbr_thread_online(struct rte_rcu_qsbr *v, unsigned int thread_id)
{
    uint64_t t;

    RTE_ASSERT(v != NULL && thread_id < v->max_threads);

    __RTE_RCU_IS_LOCK_CNT_ZERO(v, thread_id, ERR, "Lock counter %u\n",
                v->qsbr_cnt[thread_id].lock_cnt);

    /* Copy the current value of token.
     * The fence at the end of the function will ensure that
     * the following will not move down after the load of any shared
     * data structure.
     */
    t = __atomic_load_n(&v->token, __ATOMIC_RELAXED);

    /* __atomic_store_n(cnt, __ATOMIC_RELAXED) is used to ensure
     * 'cnt' (64b) is accessed atomically.
     */
    __atomic_store_n(&v->qsbr_cnt[thread_id].cnt,
        t, __ATOMIC_RELAXED);

    /* The subsequent load of the data structure should not
     * move above the store. Hence a store-load barrier
     * is required.
     * If the load of the data structure moves above the store,
     * writer might not see that the reader is online, even though
     * the reader is referencing the shared data structure.
     */
#ifdef RTE_ARCH_X86_64
    /* rte_smp_mb() for x86 is lighter */
    rte_smp_mb();
#else
    __atomic_thread_fence(__ATOMIC_SEQ_CST);
#endif
}

__rte_experimental
static __rte_always_inline void
rte_rcu_qsbr_thread_offline(struct rte_rcu_qsbr *v, unsigned int thread_id)
{
    RTE_ASSERT(v != NULL && thread_id < v->max_threads);

    __RTE_RCU_IS_LOCK_CNT_ZERO(v, thread_id, ERR, "Lock counter %u\n",
                v->qsbr_cnt[thread_id].lock_cnt);

    /* The reader can go offline only after the load of the
     * data structure is completed. i.e. any load of the
     * data strcture can not move after this store.
     */

    __atomic_store_n(&v->qsbr_cnt[thread_id].cnt,
        __RTE_QSBR_CNT_THR_OFFLINE, __ATOMIC_RELEASE);
}

__rte_experimental
static __rte_always_inline void
rte_rcu_qsbr_lock(__rte_unused struct rte_rcu_qsbr *v,
            __rte_unused unsigned int thread_id)
{
    RTE_ASSERT(v != NULL && thread_id < v->max_threads);

#if defined(RTE_LIBRTE_RCU_DEBUG)
    /* Increment the lock counter */
    __atomic_fetch_add(&v->qsbr_cnt[thread_id].lock_cnt,
                1, __ATOMIC_ACQUIRE);
#endif
}

__rte_experimental
static __rte_always_inline void
rte_rcu_qsbr_unlock(__rte_unused struct rte_rcu_qsbr *v,
            __rte_unused unsigned int thread_id)
{
    RTE_ASSERT(v != NULL && thread_id < v->max_threads);

#if defined(RTE_LIBRTE_RCU_DEBUG)
    /* Decrement the lock counter */
    __atomic_fetch_sub(&v->qsbr_cnt[thread_id].lock_cnt,
                1, __ATOMIC_RELEASE);

    __RTE_RCU_IS_LOCK_CNT_ZERO(v, thread_id, WARNING,
                "Lock counter %u. Nested locks?\n",
                v->qsbr_cnt[thread_id].lock_cnt);
#endif
}

__rte_experimental
static __rte_always_inline uint64_t
rte_rcu_qsbr_start(struct rte_rcu_qsbr *v)
{
    uint64_t t;

    RTE_ASSERT(v != NULL);

    /* Release the changes to the shared data structure.
     * This store release will ensure that changes to any data
     * structure are visible to the workers before the token
     * update is visible.
     */
    t = __atomic_add_fetch(&v->token, 1, __ATOMIC_RELEASE);

    return t;
}

__rte_experimental
static __rte_always_inline void
rte_rcu_qsbr_quiescent(struct rte_rcu_qsbr *v, unsigned int thread_id)
{
    uint64_t t;

    RTE_ASSERT(v != NULL && thread_id < v->max_threads);

    __RTE_RCU_IS_LOCK_CNT_ZERO(v, thread_id, ERR, "Lock counter %u\n",
                v->qsbr_cnt[thread_id].lock_cnt);

    /* Acquire the changes to the shared data structure released
     * by rte_rcu_qsbr_start.
     * Later loads of the shared data structure should not move
     * above this load. Hence, use load-acquire.
     */
    t = __atomic_load_n(&v->token, __ATOMIC_ACQUIRE);

    /* Check if there are updates available from the writer.
     * Inform the writer that updates are visible to this reader.
     * Prior loads of the shared data structure should not move
     * beyond this store. Hence use store-release.
     */
    if (t != __atomic_load_n(&v->qsbr_cnt[thread_id].cnt, __ATOMIC_RELAXED))
        __atomic_store_n(&v->qsbr_cnt[thread_id].cnt,
                     t, __ATOMIC_RELEASE);

    __RTE_RCU_DP_LOG(DEBUG, "%s: update: token = %"PRIu64", Thread ID = %d",
        __func__, t, thread_id);
}

/* Check the quiescent state counter for registered threads only, assuming
 * that not all threads have registered.
 */
static __rte_always_inline int
__rte_rcu_qsbr_check_selective(struct rte_rcu_qsbr *v, uint64_t t, bool wait)
{
    uint32_t i, j, id;
    uint64_t bmap;
    uint64_t c;
    uint64_t *reg_thread_id;
    uint64_t acked_token = __RTE_QSBR_CNT_MAX;

    for (i = 0, reg_thread_id = __RTE_QSBR_THRID_ARRAY_ELM(v, 0);
        i < v->num_elems;
        i++, reg_thread_id++) {
        /* Load the current registered thread bit map before
         * loading the reader thread quiescent state counters.
         */
        bmap = __atomic_load_n(reg_thread_id, __ATOMIC_ACQUIRE);
        id = i << __RTE_QSBR_THRID_INDEX_SHIFT;

        while (bmap) {
            j = __builtin_ctzl(bmap);
            __RTE_RCU_DP_LOG(DEBUG,
                "%s: check: token = %"PRIu64", wait = %d, Bit Map = 0x%"PRIx64", Thread ID = %d",
                __func__, t, wait, bmap, id + j);
            c = __atomic_load_n(
                    &v->qsbr_cnt[id + j].cnt,
                    __ATOMIC_ACQUIRE);
            __RTE_RCU_DP_LOG(DEBUG,
                "%s: status: token = %"PRIu64", wait = %d, Thread QS cnt = %"PRIu64", Thread ID = %d",
                __func__, t, wait, c, id+j);

            /* Counter is not checked for wrap-around condition
             * as it is a 64b counter.
             */
            if (unlikely(c !=
                __RTE_QSBR_CNT_THR_OFFLINE && c < t)) {
                /* This thread is not in quiescent state */
                if (!wait)
                    return 0;

                rte_pause();
                /* This thread might have unregistered.
                 * Re-read the bitmap.
                 */
                bmap = __atomic_load_n(reg_thread_id,
                        __ATOMIC_ACQUIRE);

                continue;
            }

            /* This thread is in quiescent state. Use the counter
             * to find the least acknowledged token among all the
             * readers.
             */
            if (c != __RTE_QSBR_CNT_THR_OFFLINE && acked_token > c)
                acked_token = c;

            bmap &= ~(1UL << j);
        }
    }

    /* All readers are checked, update least acknowledged token.
     * There might be multiple writers trying to update this. There is
     * no need to update this very accurately using compare-and-swap.
     */
    if (acked_token != __RTE_QSBR_CNT_MAX)
        __atomic_store_n(&v->acked_token, acked_token,
            __ATOMIC_RELAXED);

    return 1;
}

/* Check the quiescent state counter for all threads, assuming that
 * all the threads have registered.
 */
static __rte_always_inline int
__rte_rcu_qsbr_check_all(struct rte_rcu_qsbr *v, uint64_t t, bool wait)
{
    uint32_t i;
    struct rte_rcu_qsbr_cnt *cnt;
    uint64_t c;
    uint64_t acked_token = __RTE_QSBR_CNT_MAX;

    for (i = 0, cnt = v->qsbr_cnt; i < v->max_threads; i++, cnt++) {
        __RTE_RCU_DP_LOG(DEBUG,
            "%s: check: token = %"PRIu64", wait = %d, Thread ID = %d",
            __func__, t, wait, i);
        while (1) {
            c = __atomic_load_n(&cnt->cnt, __ATOMIC_ACQUIRE);
            __RTE_RCU_DP_LOG(DEBUG,
                "%s: status: token = %"PRIu64", wait = %d, Thread QS cnt = %"PRIu64", Thread ID = %d",
                __func__, t, wait, c, i);

            /* Counter is not checked for wrap-around condition
             * as it is a 64b counter.
             */
            if (likely(c == __RTE_QSBR_CNT_THR_OFFLINE || c >= t))
                break;

            /* This thread is not in quiescent state */
            if (!wait)
                return 0;

            rte_pause();
        }

        /* This thread is in quiescent state. Use the counter to find
         * the least acknowledged token among all the readers.
         */
        if (likely(c != __RTE_QSBR_CNT_THR_OFFLINE && acked_token > c))
            acked_token = c;
    }

    /* All readers are checked, update least acknowledged token.
     * There might be multiple writers trying to update this. There is
     * no need to update this very accurately using compare-and-swap.
     */
    if (acked_token != __RTE_QSBR_CNT_MAX)
        __atomic_store_n(&v->acked_token, acked_token,
            __ATOMIC_RELAXED);

    return 1;
}

__rte_experimental
static __rte_always_inline int
rte_rcu_qsbr_check(struct rte_rcu_qsbr *v, uint64_t t, bool wait)
{
    RTE_ASSERT(v != NULL);

    /* Check if all the readers have already acknowledged this token */
    if (likely(t <= v->acked_token))
        return 1;

    if (likely(v->num_threads == v->max_threads))
        return __rte_rcu_qsbr_check_all(v, t, wait);
    else
        return __rte_rcu_qsbr_check_selective(v, t, wait);
}

__rte_experimental
void
rte_rcu_qsbr_synchronize(struct rte_rcu_qsbr *v, unsigned int thread_id);

__rte_experimental
int
rte_rcu_qsbr_dump(FILE *f, struct rte_rcu_qsbr *v);

#ifdef __cplusplus
}
#endif

#endif /* _RTE_RCU_QSBR_H_ */