f7121c7b7e
-Hard set the spinlock type to uint32_t to be clearer -Switch the free/held value to a simple 0 or 1 Previously, was writing the current cpu number into the spinlock, which was only useful for debugging purposes. However, since the atomic operation was an amoswap instead of a proper CAS, it would end up overwriting the old cpu number with the new cpu number when it tried to take it. It would still work as a spinlock, since the value was !0, but it was falsely tracking which cpu actually held it. To keep it simple, just switch to 0/1 and stick with the amoswap instruction, which is much more efficient than a LR/SC pair to implement CAS on riscv. Internally still use an unsigned long for the old value, since the amoswap instruction overwrites the entire Rd register, and thus keeps the codegen efficient since it wont try to sign extend it for any comparisons afterwards. Thanks @loqoman (darwin.s.clark@gmail.com) for catching this one.
57 lines
1.2 KiB
C
57 lines
1.2 KiB
C
/*
|
|
* Copyright (c) 2015 Travis Geiselbrecht
|
|
*
|
|
* Use of this source code is governed by a MIT-style
|
|
* license that can be found in the LICENSE file or at
|
|
* https://opensource.org/licenses/MIT
|
|
*/
|
|
#include <arch/spinlock.h>
|
|
|
|
#include <stdint.h>
|
|
|
|
// super simple spin lock implementation
|
|
|
|
int riscv_spin_trylock(spin_lock_t *lock) {
|
|
// use a full 32/64 type since amoswap overwrites the entire register
|
|
unsigned long old;
|
|
|
|
__asm__ __volatile__(
|
|
"amoswap.w %0, %2, %1\n"
|
|
"fence r, rw\n"
|
|
: "=r"(old), "+A"(*lock)
|
|
: "r" (1u)
|
|
: "memory"
|
|
);
|
|
|
|
return !old;
|
|
}
|
|
|
|
void riscv_spin_lock(spin_lock_t *lock) {
|
|
for (;;) {
|
|
if (*lock) {
|
|
// TODO: use a yield instruction here?
|
|
continue;
|
|
}
|
|
|
|
// use a full 32/64 type since amoswap overwrites the entire register
|
|
unsigned long old;
|
|
__asm__ __volatile__(
|
|
"amoswap.w %0, %2, %1\n"
|
|
"fence r, rw\n"
|
|
: "=r"(old), "+A"(*lock)
|
|
: "r" (1u)
|
|
: "memory"
|
|
);
|
|
|
|
if (!old) {
|
|
break;
|
|
}
|
|
}
|
|
}
|
|
|
|
void riscv_spin_unlock(spin_lock_t *lock) {
|
|
__asm__ volatile("fence rw,w" ::: "memory");
|
|
*lock = 0;
|
|
}
|
|
|