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Diffstat (limited to 'include/ck_ec.h')
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diff --git a/include/ck_ec.h b/include/ck_ec.h new file mode 100644 index 000000000000..cd2a36813a79 --- /dev/null +++ b/include/ck_ec.h @@ -0,0 +1,945 @@ +/* + * Copyright 2018 Paul Khuong, Google LLC. + * All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. 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. + * + * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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. + */ + +/* + * Overview + * ======== + * + * ck_ec implements 32- and 64- bit event counts. Event counts let us + * easily integrate OS-level blocking (e.g., futexes) in lock-free + * protocols. Waiters block conditionally, if the event count's value + * is still equal to some old value. + * + * Event counts come in four variants: 32 and 64 bit (with one bit + * stolen for internal signaling, so 31 and 63 bit counters), and + * single or multiple producers (wakers). Waiters are always multiple + * consumers. The 32 bit variants are smaller, and more efficient, + * especially in single producer mode. The 64 bit variants are larger, + * but practically invulnerable to ABA. + * + * The 32 bit variant is always available. The 64 bit variant is only + * available if CK supports 64-bit atomic operations. Currently, + * specialization for single producer is only implemented for x86 and + * x86-64, on compilers that support GCC extended inline assembly; + * other platforms fall back to the multiple producer code path. + * + * A typical usage pattern is: + * + * 1. On the producer side: + * + * - Make changes to some shared data structure, without involving + * the event count at all. + * - After each change, call ck_ec_inc on the event count. The call + * acts as a write-write barrier, and wakes up any consumer blocked + * on the event count (waiting for new changes). + * + * 2. On the consumer side: + * + * - Snapshot ck_ec_value of the event count. The call acts as a + * read barrier. + * - Read and process the shared data structure. + * - Wait for new changes by calling ck_ec_wait with the snapshot value. + * + * Some data structures may opt for tighter integration with their + * event count. For example, an SPMC ring buffer or disruptor might + * use the event count's value as the write pointer. If the buffer is + * regularly full, it might also make sense to store the read pointer + * in an MP event count. + * + * This event count implementation supports tighter integration in two + * ways. + * + * Producers may opt to increment by an arbitrary value (less than + * INT32_MAX / INT64_MAX), in order to encode, e.g., byte + * offsets. Larger increment values make wraparound more likely, so + * the increments should still be relatively small. + * + * Consumers may pass a predicate to ck_ec_wait_pred. This predicate + * can make `ck_ec_wait_pred` return early, before the event count's + * value changes, and can override the deadline passed to futex_wait. + * This lets consumer block on one eventcount, while optimistically + * looking at other waking conditions. + * + * API Reference + * ============= + * + * When compiled as C11 or later, this header defines type-generic + * macros for ck_ec32 and ck_ec64; the reference describes this + * type-generic API. + * + * ck_ec needs additional OS primitives to determine the current time, + * to wait on an address, and to wake all threads waiting on a given + * address. These are defined with fields in a struct ck_ec_ops. Each + * ck_ec_ops may additionally define the number of spin loop + * iterations in the slow path, as well as the initial wait time in + * the internal exponential backoff, the exponential scale factor, and + * the right shift count (< 32). + * + * The ops, in addition to the single/multiple producer flag, are + * encapsulated in a struct ck_ec_mode, passed to most ck_ec + * operations. + * + * ec is a struct ck_ec32 *, or a struct ck_ec64 *. + * + * value is an uint32_t for ck_ec32, and an uint64_t for ck_ec64. It + * never exceeds INT32_MAX and INT64_MAX respectively. + * + * mode is a struct ck_ec_mode *. + * + * deadline is either NULL, or a `const struct timespec *` that will + * be treated as an absolute deadline. + * + * `void ck_ec_init(ec, value)`: initializes the event count to value. + * + * `value ck_ec_value(ec)`: returns the current value of the event + * counter. This read acts as a read (acquire) barrier. + * + * `bool ck_ec_has_waiters(ec)`: returns whether some thread has + * marked the event count as requiring an OS wakeup. + * + * `void ck_ec_inc(ec, mode)`: increments the value of the event + * counter by one. This writes acts as a write barrier. Wakes up + * any waiting thread. + * + * `value ck_ec_add(ec, mode, value)`: increments the event counter by + * `value`, and returns the event counter's previous value. This + * write acts as a write barrier. Wakes up any waiting thread. + * + * `int ck_ec_deadline(struct timespec *new_deadline, + * mode, + * const struct timespec *timeout)`: + * computes a deadline `timeout` away from the current time. If + * timeout is NULL, computes a deadline in the infinite future. The + * resulting deadline is written to `new_deadline`. Returns 0 on + * success, and -1 if ops->gettime failed (without touching errno). + * + * `int ck_ec_wait(ec, mode, value, deadline)`: waits until the event + * counter's value differs from `value`, or, if `deadline` is + * provided and non-NULL, until the current time is after that + * deadline. Use a deadline with tv_sec = 0 for a non-blocking + * execution. Returns 0 if the event counter has changed, and -1 on + * timeout. This function acts as a read (acquire) barrier. + * + * `int ck_ec_wait_pred(ec, mode, value, pred, data, deadline)`: waits + * until the event counter's value differs from `value`, or until + * `pred` returns non-zero, or, if `deadline` is provided and + * non-NULL, until the current time is after that deadline. Use a + * deadline with tv_sec = 0 for a non-blocking execution. Returns 0 if + * the event counter has changed, `pred`'s return value if non-zero, + * and -1 on timeout. This function acts as a read (acquire) barrier. + * + * `pred` is always called as `pred(data, iteration_deadline, now)`, + * where `iteration_deadline` is a timespec of the deadline for this + * exponential backoff iteration, and `now` is the current time. If + * `pred` returns a non-zero value, that value is immediately returned + * to the waiter. Otherwise, `pred` is free to modify + * `iteration_deadline` (moving it further in the future is a bad + * idea). + * + * Implementation notes + * ==================== + * + * The multiple producer implementation is a regular locked event + * count, with a single flag bit to denote the need to wake up waiting + * threads. + * + * The single producer specialization is heavily tied to + * [x86-TSO](https://www.cl.cam.ac.uk/~pes20/weakmemory/cacm.pdf), and + * to non-atomic read-modify-write instructions (e.g., `inc mem`); + * these non-atomic RMW let us write to the same memory locations with + * atomic and non-atomic instructions, without suffering from process + * scheduling stalls. + * + * The reason we can mix atomic and non-atomic writes to the `counter` + * word is that every non-atomic write obviates the need for the + * atomically flipped flag bit: we only use non-atomic writes to + * update the event count, and the atomic flag only informs the + * producer that we would like a futex_wake, because of the update. + * We only require the non-atomic RMW counter update to prevent + * preemption from introducing arbitrarily long worst case delays. + * + * Correctness does not rely on the usual ordering argument: in the + * absence of fences, there is no strict ordering between atomic and + * non-atomic writes. The key is instead x86-TSO's guarantee that a + * read is satisfied from the most recent buffered write in the local + * store queue if there is one, or from memory if there is no write to + * that address in the store queue. + * + * x86-TSO's constraint on reads suffices to guarantee that the + * producer will never forget about a counter update. If the last + * update is still queued, the new update will be based on the queued + * value. Otherwise, the new update will be based on the value in + * memory, which may or may not have had its flag flipped. In either + * case, the value of the counter (modulo flag) is correct. + * + * When the producer forwards the counter's value from its store + * queue, the new update might not preserve a flag flip. Any waiter + * thus has to check from time to time to determine if it wasn't + * woken up because the flag bit was silently cleared. + * + * In reality, the store queue in x86-TSO stands for in-flight + * instructions in the chip's out-of-order backend. In the vast + * majority of cases, instructions will only remain in flight for a + * few hundred or thousand of cycles. That's why ck_ec_wait spins on + * the `counter` word for ~100 iterations after flipping its flag bit: + * if the counter hasn't changed after that many iterations, it is + * very likely that the producer's next counter update will observe + * the flag flip. + * + * That's still not a hard guarantee of correctness. Conservatively, + * we can expect that no instruction will remain in flight for more + * than 1 second... if only because some interrupt will have forced + * the chip to store its architectural state in memory, at which point + * an instruction is either fully retired or rolled back. Interrupts, + * particularly the pre-emption timer, are why single-producer updates + * must happen in a single non-atomic read-modify-write instruction. + * Having a single instruction as the critical section means we only + * have to consider the worst-case execution time for that + * instruction. That's easier than doing the same for a pair of + * instructions, which an unlucky pre-emption could delay for + * arbitrarily long. + * + * Thus, after a short spin loop, ck_ec_wait enters an exponential + * backoff loop, where each "sleep" is instead a futex_wait. The + * backoff is only necessary to handle rare cases where the flag flip + * was overwritten after the spin loop. Eventually, more than one + * second will have elapsed since the flag flip, and the sleep timeout + * becomes infinite: since the flag bit has been set for much longer + * than the time for which an instruction may remain in flight, the + * flag will definitely be observed at the next counter update. + * + * The 64 bit ck_ec_wait pulls another trick: futexes only handle 32 + * bit ints, so we must treat the 64 bit counter's low 32 bits as an + * int in futex_wait. That's a bit dodgy, but fine in practice, given + * that the OS's futex code will always read whatever value is + * currently in memory: even if the producer thread were to wait on + * its own event count, the syscall and ring transition would empty + * the store queue (the out-of-order execution backend). + * + * Finally, what happens when the producer is migrated to another core + * or otherwise pre-empted? Migration must already incur a barrier, so + * that thread always sees its own writes, so that's safe. As for + * pre-emption, that requires storing the architectural state, which + * means every instruction must either be executed fully or not at + * all when pre-emption happens. + */ + +#ifndef CK_EC_H +#define CK_EC_H +#include <ck_cc.h> +#include <ck_pr.h> +#include <ck_stdbool.h> +#include <ck_stdint.h> +#include <ck_stddef.h> +#include <sys/time.h> + +/* + * If we have ck_pr_faa_64 (and, presumably, ck_pr_load_64), we + * support 63 bit counters. + */ +#ifdef CK_F_PR_FAA_64 +#define CK_F_EC64 +#endif /* CK_F_PR_FAA_64 */ + +/* + * GCC inline assembly lets us exploit non-atomic read-modify-write + * instructions on x86/x86_64 for a fast single-producer mode. + * + * If we CK_F_EC_SP is not defined, CK_EC always uses the slower + * multiple producer code. + */ +#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) +#define CK_F_EC_SP +#endif /* GNUC && (__i386__ || __x86_64__) */ + +struct ck_ec_ops; + +struct ck_ec_wait_state { + struct timespec start; /* Time when we entered ck_ec_wait. */ + struct timespec now; /* Time now. */ + const struct ck_ec_ops *ops; + void *data; /* Opaque pointer for the predicate's internal state. */ + +}; + +/* + * ck_ec_ops define system-specific functions to get the current time, + * atomically wait on an address if it still has some expected value, + * and to wake all threads waiting on an address. + * + * Each platform is expected to have few (one) opaque pointer to a + * const ops struct, and reuse it for all ck_ec_mode structs. + */ +struct ck_ec_ops { + /* Populates out with the current time. Returns non-zero on failure. */ + int (*gettime)(const struct ck_ec_ops *, struct timespec *out); + + /* + * Waits on address if its value is still `expected`. If + * deadline is non-NULL, stops waiting once that deadline is + * reached. May return early for any reason. + */ + void (*wait32)(const struct ck_ec_wait_state *, const uint32_t *, + uint32_t expected, const struct timespec *deadline); + + /* + * Same as wait32, but for a 64 bit counter. Only used if + * CK_F_EC64 is defined. + * + * If underlying blocking primitive only supports 32 bit + * control words, it should be safe to block on the least + * significant half of the 64 bit address. + */ + void (*wait64)(const struct ck_ec_wait_state *, const uint64_t *, + uint64_t expected, const struct timespec *deadline); + + /* Wakes up all threads waiting on address. */ + void (*wake32)(const struct ck_ec_ops *, const uint32_t *address); + + /* + * Same as wake32, but for a 64 bit counter. Only used if + * CK_F_EC64 is defined. + * + * When wait64 truncates the control word at address to `only` + * consider its least significant half, wake64 should perform + * any necessary fixup (e.g., on big endian platforms). + */ + void (*wake64)(const struct ck_ec_ops *, const uint64_t *address); + + /* + * Number of iterations for the initial busy wait. 0 defaults + * to 100 (not ABI stable). + */ + uint32_t busy_loop_iter; + + /* + * Delay in nanoseconds for the first iteration of the + * exponential backoff. 0 defaults to 2 ms (not ABI stable). + */ + uint32_t initial_wait_ns; + + /* + * Scale factor for the exponential backoff. 0 defaults to 8x + * (not ABI stable). + */ + uint32_t wait_scale_factor; + + /* + * Right shift count for the exponential backoff. The update + * after each iteration is + * wait_ns = (wait_ns * wait_scale_factor) >> wait_shift_count, + * until one second has elapsed. After that, the deadline goes + * to infinity. + */ + uint32_t wait_shift_count; +}; + +/* + * ck_ec_mode wraps the ops table, and informs the fast path whether + * it should attempt to specialize for single producer mode. + * + * mode structs are expected to be exposed by value, e.g., + * + * extern const struct ck_ec_ops system_ec_ops; + * + * static const struct ck_ec_mode ec_sp = { + * .ops = &system_ec_ops, + * .single_producer = true + * }; + * + * static const struct ck_ec_mode ec_mp = { + * .ops = &system_ec_ops, + * .single_producer = false + * }; + * + * ck_ec_mode structs are only passed to inline functions defined in + * this header, and never escape to their slow paths, so they should + * not result in any object file size increase. + */ +struct ck_ec_mode { + const struct ck_ec_ops *ops; + /* + * If single_producer is true, the event count has a unique + * incrementer. The implementation will specialize ck_ec_inc + * and ck_ec_add if possible (if CK_F_EC_SP is defined). + */ + bool single_producer; +}; + +struct ck_ec32 { + /* Flag is "sign" bit, value in bits 0:30. */ + uint32_t counter; +}; + +typedef struct ck_ec32 ck_ec32_t; + +#ifdef CK_F_EC64 +struct ck_ec64 { + /* + * Flag is bottom bit, value in bits 1:63. Eventcount only + * works on x86-64 (i.e., little endian), so the futex int + * lies in the first 4 (bottom) bytes. + */ + uint64_t counter; +}; + +typedef struct ck_ec64 ck_ec64_t; +#endif /* CK_F_EC64 */ + +#define CK_EC_INITIALIZER { .counter = 0 } + +/* + * Initializes the event count to `value`. The value must not + * exceed INT32_MAX. + */ +static void ck_ec32_init(struct ck_ec32 *ec, uint32_t value); + +#ifndef CK_F_EC64 +#define ck_ec_init ck_ec32_init +#else +/* + * Initializes the event count to `value`. The value must not + * exceed INT64_MAX. + */ +static void ck_ec64_init(struct ck_ec64 *ec, uint64_t value); + +#if __STDC_VERSION__ >= 201112L +#define ck_ec_init(EC, VALUE) \ + (_Generic(*(EC), \ + struct ck_ec32 : ck_ec32_init, \ + struct ck_ec64 : ck_ec64_init)((EC), (VALUE))) +#endif /* __STDC_VERSION__ */ +#endif /* CK_F_EC64 */ + +/* + * Returns the counter value in the event count. The value is at most + * INT32_MAX. + */ +static uint32_t ck_ec32_value(const struct ck_ec32* ec); + +#ifndef CK_F_EC64 +#define ck_ec_value ck_ec32_value +#else +/* + * Returns the counter value in the event count. The value is at most + * INT64_MAX. + */ +static uint64_t ck_ec64_value(const struct ck_ec64* ec); + +#if __STDC_VERSION__ >= 201112L +#define ck_ec_value(EC) \ + (_Generic(*(EC), \ + struct ck_ec32 : ck_ec32_value, \ + struct ck_ec64 : ck_ec64_value)((EC))) +#endif /* __STDC_VERSION__ */ +#endif /* CK_F_EC64 */ + +/* + * Returns whether there may be slow pathed waiters that need an + * explicit OS wakeup for this event count. + */ +static bool ck_ec32_has_waiters(const struct ck_ec32 *ec); + +#ifndef CK_F_EC64 +#define ck_ec_has_waiters ck_ec32_has_waiters +#else +static bool ck_ec64_has_waiters(const struct ck_ec64 *ec); + +#if __STDC_VERSION__ >= 201112L +#define ck_ec_has_waiters(EC) \ + (_Generic(*(EC), \ + struct ck_ec32 : ck_ec32_has_waiters, \ + struct ck_ec64 : ck_ec64_has_waiters)((EC))) +#endif /* __STDC_VERSION__ */ +#endif /* CK_F_EC64 */ + +/* + * Increments the counter value in the event count by one, and wakes + * up any waiter. + */ +static void ck_ec32_inc(struct ck_ec32 *ec, const struct ck_ec_mode *mode); + +#ifndef CK_F_EC64 +#define ck_ec_inc ck_ec32_inc +#else +static void ck_ec64_inc(struct ck_ec64 *ec, const struct ck_ec_mode *mode); + +#if __STDC_VERSION__ >= 201112L +#define ck_ec_inc(EC, MODE) \ + (_Generic(*(EC), \ + struct ck_ec32 : ck_ec32_inc, \ + struct ck_ec64 : ck_ec64_inc)((EC), (MODE))) +#endif /* __STDC_VERSION__ */ +#endif /* CK_F_EC64 */ + +/* + * Increments the counter value in the event count by delta, wakes + * up any waiter, and returns the previous counter value. + */ +static uint32_t ck_ec32_add(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t delta); + +#ifndef CK_F_EC64 +#define ck_ec_add ck_ec32_add +#else +static uint64_t ck_ec64_add(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t delta); + +#if __STDC_VERSION__ >= 201112L +#define ck_ec_add(EC, MODE, DELTA) \ + (_Generic(*(EC), \ + struct ck_ec32 : ck_ec32_add, \ + struct ck_ec64 : ck_ec64_add)((EC), (MODE), (DELTA))) +#endif /* __STDC_VERSION__ */ +#endif /* CK_F_EC64 */ + +/* + * Populates `new_deadline` with a deadline `timeout` in the future. + * Returns 0 on success, and -1 if clock_gettime failed, in which + * case errno is left as is. + */ +static int ck_ec_deadline(struct timespec *new_deadline, + const struct ck_ec_mode *mode, + const struct timespec *timeout); + +/* + * Waits until the counter value in the event count differs from + * old_value, or, if deadline is non-NULL, until CLOCK_MONOTONIC is + * past the deadline. + * + * Returns 0 on success, and -1 on timeout. + */ +static int ck_ec32_wait(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t old_value, + const struct timespec *deadline); + +#ifndef CK_F_EC64 +#define ck_ec_wait ck_ec32_wait +#else +static int ck_ec64_wait(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t old_value, + const struct timespec *deadline); + +#if __STDC_VERSION__ >= 201112L +#define ck_ec_wait(EC, MODE, OLD_VALUE, DEADLINE) \ + (_Generic(*(EC), \ + struct ck_ec32 : ck_ec32_wait, \ + struct ck_ec64 : ck_ec64_wait)((EC), (MODE), \ + (OLD_VALUE), (DEADLINE))) + +#endif /* __STDC_VERSION__ */ +#endif /* CK_F_EC64 */ + +/* + * Waits until the counter value in the event count differs from + * old_value, pred returns non-zero, or, if deadline is non-NULL, + * until CLOCK_MONOTONIC is past the deadline. + * + * Returns 0 on success, -1 on timeout, and the return value of pred + * if it returns non-zero. + * + * A NULL pred represents a function that always returns 0. + */ +static int ck_ec32_wait_pred(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t old_value, + int (*pred)(const struct ck_ec_wait_state *, + struct timespec *deadline), + void *data, + const struct timespec *deadline); + +#ifndef CK_F_EC64 +#define ck_ec_wait_pred ck_ec32_wait_pred +#else +static int ck_ec64_wait_pred(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t old_value, + int (*pred)(const struct ck_ec_wait_state *, + struct timespec *deadline), + void *data, + const struct timespec *deadline); + +#if __STDC_VERSION__ >= 201112L +#define ck_ec_wait_pred(EC, MODE, OLD_VALUE, PRED, DATA, DEADLINE) \ + (_Generic(*(EC), \ + struct ck_ec32 : ck_ec32_wait_pred, \ + struct ck_ec64 : ck_ec64_wait_pred) \ + ((EC), (MODE), (OLD_VALUE), (PRED), (DATA), (DEADLINE))) +#endif /* __STDC_VERSION__ */ +#endif /* CK_F_EC64 */ + +/* + * Inline implementation details. 32 bit first, then 64 bit + * conditionally. + */ +CK_CC_FORCE_INLINE void ck_ec32_init(struct ck_ec32 *ec, uint32_t value) +{ + ec->counter = value & ~(1UL << 31); + return; +} + +CK_CC_FORCE_INLINE uint32_t ck_ec32_value(const struct ck_ec32 *ec) +{ + uint32_t ret = ck_pr_load_32(&ec->counter) & ~(1UL << 31); + + ck_pr_fence_acquire(); + return ret; +} + +CK_CC_FORCE_INLINE bool ck_ec32_has_waiters(const struct ck_ec32 *ec) +{ + return ck_pr_load_32(&ec->counter) & (1UL << 31); +} + +/* Slow path for ck_ec{32,64}_{inc,add} */ +void ck_ec32_wake(struct ck_ec32 *ec, const struct ck_ec_ops *ops); + +CK_CC_FORCE_INLINE void ck_ec32_inc(struct ck_ec32 *ec, + const struct ck_ec_mode *mode) +{ +#if !defined(CK_F_EC_SP) + /* Nothing to specialize if we don't have EC_SP. */ + ck_ec32_add(ec, mode, 1); + return; +#else + char flagged; + +#if __GNUC__ >= 6 + /* + * We don't want to wake if the sign bit is 0. We do want to + * wake if the sign bit just flipped from 1 to 0. We don't + * care what happens when our increment caused the sign bit to + * flip from 0 to 1 (that's once per 2^31 increment). + * + * This leaves us with four cases: + * + * old sign bit | new sign bit | SF | OF | ZF + * ------------------------------------------- + * 0 | 0 | 0 | 0 | ? + * 0 | 1 | 1 | 0 | ? + * 1 | 1 | 1 | 0 | ? + * 1 | 0 | 0 | 0 | 1 + * + * In the first case, we don't want to hit ck_ec32_wake. In + * the last two cases, we do want to call ck_ec32_wake. In the + * second case, we don't care, so we arbitrarily choose to + * call ck_ec32_wake. + * + * The "le" condition checks if SF != OF, or ZF == 1, which + * meets our requirements. + */ +#define CK_EC32_INC_ASM(PREFIX) \ + __asm__ volatile(PREFIX " incl %0" \ + : "+m"(ec->counter), "=@ccle"(flagged) \ + :: "cc", "memory") +#else +#define CK_EC32_INC_ASM(PREFIX) \ + __asm__ volatile(PREFIX " incl %0; setle %1" \ + : "+m"(ec->counter), "=r"(flagged) \ + :: "cc", "memory") +#endif /* __GNUC__ */ + + if (mode->single_producer == true) { + ck_pr_fence_store(); + CK_EC32_INC_ASM(""); + } else { + ck_pr_fence_store_atomic(); + CK_EC32_INC_ASM("lock"); + } +#undef CK_EC32_INC_ASM + + if (CK_CC_UNLIKELY(flagged)) { + ck_ec32_wake(ec, mode->ops); + } + + return; +#endif /* CK_F_EC_SP */ +} + +CK_CC_FORCE_INLINE uint32_t ck_ec32_add_epilogue(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t old) +{ + const uint32_t flag_mask = 1U << 31; + uint32_t ret; + + ret = old & ~flag_mask; + /* These two only differ if the flag bit is set. */ + if (CK_CC_UNLIKELY(old != ret)) { + ck_ec32_wake(ec, mode->ops); + } + + return ret; +} + +static CK_CC_INLINE uint32_t ck_ec32_add_mp(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t delta) +{ + uint32_t old; + + ck_pr_fence_store_atomic(); + old = ck_pr_faa_32(&ec->counter, delta); + return ck_ec32_add_epilogue(ec, mode, old); +} + +#ifdef CK_F_EC_SP +static CK_CC_INLINE uint32_t ck_ec32_add_sp(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t delta) +{ + uint32_t old; + + /* + * Correctness of this racy write depends on actually + * having an update to write. Exit here if the update + * is a no-op. + */ + if (CK_CC_UNLIKELY(delta == 0)) { + return ck_ec32_value(ec); + } + + ck_pr_fence_store(); + old = delta; + __asm__ volatile("xaddl %1, %0" + : "+m"(ec->counter), "+r"(old) + :: "cc", "memory"); + return ck_ec32_add_epilogue(ec, mode, old); +} +#endif /* CK_F_EC_SP */ + +CK_CC_FORCE_INLINE uint32_t ck_ec32_add(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t delta) +{ +#ifdef CK_F_EC_SP + if (mode->single_producer == true) { + return ck_ec32_add_sp(ec, mode, delta); + } +#endif + + return ck_ec32_add_mp(ec, mode, delta); +} + +int ck_ec_deadline_impl(struct timespec *new_deadline, + const struct ck_ec_ops *ops, + const struct timespec *timeout); + +CK_CC_FORCE_INLINE int ck_ec_deadline(struct timespec *new_deadline, + const struct ck_ec_mode *mode, + const struct timespec *timeout) +{ + return ck_ec_deadline_impl(new_deadline, mode->ops, timeout); +} + + +int ck_ec32_wait_slow(struct ck_ec32 *ec, + const struct ck_ec_ops *ops, + uint32_t old_value, + const struct timespec *deadline); + +CK_CC_FORCE_INLINE int ck_ec32_wait(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t old_value, + const struct timespec *deadline) +{ + if (ck_ec32_value(ec) != old_value) { + return 0; + } + + return ck_ec32_wait_slow(ec, mode->ops, old_value, deadline); +} + +int ck_ec32_wait_pred_slow(struct ck_ec32 *ec, + const struct ck_ec_ops *ops, + uint32_t old_value, + int (*pred)(const struct ck_ec_wait_state *state, + struct timespec *deadline), + void *data, + const struct timespec *deadline); + +CK_CC_FORCE_INLINE int +ck_ec32_wait_pred(struct ck_ec32 *ec, + const struct ck_ec_mode *mode, + uint32_t old_value, + int (*pred)(const struct ck_ec_wait_state *state, + struct timespec *deadline), + void *data, + const struct timespec *deadline) +{ + if (ck_ec32_value(ec) != old_value) { + return 0; + } + + return ck_ec32_wait_pred_slow(ec, mode->ops, old_value, + pred, data, deadline); +} + +#ifdef CK_F_EC64 +CK_CC_FORCE_INLINE void ck_ec64_init(struct ck_ec64 *ec, uint64_t value) +{ + ec->counter = value << 1; + return; +} + +CK_CC_FORCE_INLINE uint64_t ck_ec64_value(const struct ck_ec64 *ec) +{ + uint64_t ret = ck_pr_load_64(&ec->counter) >> 1; + + ck_pr_fence_acquire(); + return ret; +} + +CK_CC_FORCE_INLINE bool ck_ec64_has_waiters(const struct ck_ec64 *ec) +{ + return ck_pr_load_64(&ec->counter) & 1; +} + +void ck_ec64_wake(struct ck_ec64 *ec, const struct ck_ec_ops *ops); + +CK_CC_FORCE_INLINE void ck_ec64_inc(struct ck_ec64 *ec, + const struct ck_ec_mode *mode) +{ + /* We always xadd, so there's no special optimization here. */ + (void)ck_ec64_add(ec, mode, 1); + return; +} + +CK_CC_FORCE_INLINE uint64_t ck_ec_add64_epilogue(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t old) +{ + uint64_t ret = old >> 1; + + if (CK_CC_UNLIKELY(old & 1)) { + ck_ec64_wake(ec, mode->ops); + } + + return ret; +} + +static CK_CC_INLINE uint64_t ck_ec64_add_mp(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t delta) +{ + uint64_t inc = 2 * delta; /* The low bit is the flag bit. */ + + ck_pr_fence_store_atomic(); + return ck_ec_add64_epilogue(ec, mode, ck_pr_faa_64(&ec->counter, inc)); +} + +#ifdef CK_F_EC_SP +/* Single-producer specialisation. */ +static CK_CC_INLINE uint64_t ck_ec64_add_sp(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t delta) +{ + uint64_t old; + + /* + * Correctness of this racy write depends on actually + * having an update to write. Exit here if the update + * is a no-op. + */ + if (CK_CC_UNLIKELY(delta == 0)) { + return ck_ec64_value(ec); + } + + ck_pr_fence_store(); + old = 2 * delta; /* The low bit is the flag bit. */ + __asm__ volatile("xaddq %1, %0" + : "+m"(ec->counter), "+r"(old) + :: "cc", "memory"); + return ck_ec_add64_epilogue(ec, mode, old); +} +#endif /* CK_F_EC_SP */ + +/* + * Dispatch on mode->single_producer in this FORCE_INLINE function: + * the end result is always small, but not all compilers have enough + * foresight to inline and get the reduction. + */ +CK_CC_FORCE_INLINE uint64_t ck_ec64_add(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t delta) +{ +#ifdef CK_F_EC_SP + if (mode->single_producer == true) { + return ck_ec64_add_sp(ec, mode, delta); + } +#endif + + return ck_ec64_add_mp(ec, mode, delta); +} + +int ck_ec64_wait_slow(struct ck_ec64 *ec, + const struct ck_ec_ops *ops, + uint64_t old_value, + const struct timespec *deadline); + +CK_CC_FORCE_INLINE int ck_ec64_wait(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t old_value, + const struct timespec *deadline) +{ + if (ck_ec64_value(ec) != old_value) { + return 0; + } + + return ck_ec64_wait_slow(ec, mode->ops, old_value, deadline); +} + +int ck_ec64_wait_pred_slow(struct ck_ec64 *ec, + const struct ck_ec_ops *ops, + uint64_t old_value, + int (*pred)(const struct ck_ec_wait_state *state, + struct timespec *deadline), + void *data, + const struct timespec *deadline); + + +CK_CC_FORCE_INLINE int +ck_ec64_wait_pred(struct ck_ec64 *ec, + const struct ck_ec_mode *mode, + uint64_t old_value, + int (*pred)(const struct ck_ec_wait_state *state, + struct timespec *deadline), + void *data, + const struct timespec *deadline) +{ + if (ck_ec64_value(ec) != old_value) { + return 0; + } + + return ck_ec64_wait_pred_slow(ec, mode->ops, old_value, + pred, data, deadline); +} +#endif /* CK_F_EC64 */ +#endif /* !CK_EC_H */ |