105 lines
2.7 KiB
C++
105 lines
2.7 KiB
C++
/*
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* \brief Nova specific user land "Spin lock" implementation
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* \author Alexander Boettcher
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* \date 2014-02-07
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*/
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/*
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* Copyright (C) 2014-2014 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU General Public License version 2.
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*/
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#ifndef _INCLUDE__BASE__LOCK__SPIN_H_
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#define _INCLUDE__BASE__LOCK__SPIN_H_
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/* Genode includes */
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#include <cpu/atomic.h>
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#include <cpu/memory_barrier.h>
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#include <base/thread.h>
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/* base-internal includes */
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#include <base/internal/lock_helper.h>
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enum State {
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SPINLOCK_LOCKED = 0, SPINLOCK_UNLOCKED = 1, SPINLOCK_CONTENDED = 2,
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};
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enum { RESERVED_BITS = 12, COUNTER_MASK = 0xFFC };
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template <typename T>
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static inline void spinlock_lock(volatile T *lock_variable)
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{
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using Genode::cmpxchg;
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Genode::Thread_base * myself = Genode::Thread_base::myself();
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T const tid = myself ? myself->tid().ec_sel : Nova::PT_SEL_MAIN_EC;
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unsigned help_counter = 0;
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/* sanity check that ec_sel fits into the lock_variable */
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if (tid >= (1 << (sizeof(*lock_variable) * 8 - RESERVED_BITS)))
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nova_die();
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if (myself) {
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Nova::Utcb * utcb = reinterpret_cast<Nova::Utcb *>(myself->utcb());
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help_counter = utcb->tls & COUNTER_MASK;
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}
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/* try to get lock */
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do {
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T raw = *lock_variable;
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if (raw != SPINLOCK_UNLOCKED) {
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if (!(raw & SPINLOCK_CONTENDED))
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/* if it fails - just re-read and retry */
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if (!Genode::cmpxchg(lock_variable, raw, raw | SPINLOCK_CONTENDED))
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continue;
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/*
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* Donate remaining time slice to help the spinlock holder to
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* pass the critical section.
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*/
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unsigned long const ec = raw >> RESERVED_BITS;
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unsigned long const tls = raw & COUNTER_MASK;
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Nova::ec_ctrl(Nova::EC_DONATE_SC, ec, tls);
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continue;
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}
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} while (!cmpxchg(lock_variable, (T)SPINLOCK_UNLOCKED,
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(tid << RESERVED_BITS) | help_counter | SPINLOCK_LOCKED));
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}
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template <typename T>
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static inline void spinlock_unlock(volatile T *lock_variable)
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{
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using Nova::Utcb;
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Genode::Thread_base * myself = Genode::Thread_base::myself();
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Utcb * utcb = myself ? reinterpret_cast<Utcb *>(myself->utcb()) : 0;
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/* unlock */
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T old;
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do {
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old = *lock_variable;
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} while (!Genode::cmpxchg(lock_variable, old, (T)SPINLOCK_UNLOCKED));
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/* de-flag time donation help request and set new counter */
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if (utcb) {
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utcb->tls = (((utcb->tls & COUNTER_MASK) + 4) % 4096) & COUNTER_MASK;
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/* take care that compiler generates code that writes tls to memory */
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Genode::memory_barrier();
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}
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/*
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* If anybody donated time, request kernel for a re-schedule in order that
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* the helper can get its time donation (SC) back.
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*/
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if (old & SPINLOCK_CONTENDED)
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Nova::ec_ctrl(Nova::EC_RESCHEDULE);
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}
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#endif /* _INCLUDE__BASE__LOCK__SPIN_H_ */
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