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[Qemu-devel] [RFC 02/30] tcg: add tcg_cmpxchg_lock
From: |
Emilio G. Cota |
Subject: |
[Qemu-devel] [RFC 02/30] tcg: add tcg_cmpxchg_lock |
Date: |
Mon, 27 Jun 2016 15:01:48 -0400 |
This set of locks will allow us to correctly emulate cmpxchg16
in a parallel TCG. The key observation is that no architecture
supports 16-byte regular atomic load/stores; only "locked" accesses
(e.g. via cmpxchg16b on x86) are allowed, and therefore we can emulate
them by using locks.
We use a small array of locks so that we can have some scalability.
Further improvements are possible (e.g. using a radix tree); but
we should have a workload to benchmark in order to justify the
additional complexity.
Signed-off-by: Emilio G. Cota <address@hidden>
---
cpu-exec.c | 1 +
linux-user/main.c | 1 +
tcg/tcg.h | 5 +++++
translate-all.c | 39 +++++++++++++++++++++++++++++++++++++++
4 files changed, 46 insertions(+)
diff --git a/cpu-exec.c b/cpu-exec.c
index b840e1d..26f3bd6 100644
--- a/cpu-exec.c
+++ b/cpu-exec.c
@@ -643,6 +643,7 @@ int cpu_exec(CPUState *cpu)
#endif /* buggy compiler */
cpu->can_do_io = 1;
tb_lock_reset();
+ tcg_cmpxchg_lock_reset();
}
} /* for(;;) */
diff --git a/linux-user/main.c b/linux-user/main.c
index 78d8d04..af9e8e3 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -140,6 +140,7 @@ void fork_end(int child)
pthread_cond_init(&exclusive_cond, NULL);
pthread_cond_init(&exclusive_resume, NULL);
qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock);
+ tcg_cmpxchg_lock_init();
gdbserver_fork(thread_cpu);
} else {
pthread_mutex_unlock(&exclusive_lock);
diff --git a/tcg/tcg.h b/tcg/tcg.h
index 1fd7ec3..1c9c8bc 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -650,6 +650,11 @@ void tb_lock(void);
void tb_unlock(void);
void tb_lock_reset(void);
+void tcg_cmpxchg_lock(uintptr_t addr);
+void tcg_cmpxchg_unlock(void);
+void tcg_cmpxchg_lock_reset(void);
+void tcg_cmpxchg_lock_init(void);
+
static inline void *tcg_malloc(int size)
{
TCGContext *s = &tcg_ctx;
diff --git a/translate-all.c b/translate-all.c
index eaa95e4..19432e5 100644
--- a/translate-all.c
+++ b/translate-all.c
@@ -153,6 +153,44 @@ void tb_lock_reset(void)
#endif
}
+#define TCG_CMPXCHG_NR_LOCKS 16
+static QemuMutex tcg_cmpxchg_locks[TCG_CMPXCHG_NR_LOCKS];
+static __thread QemuMutex *tcg_cmpxchg_curr_lock;
+
+void tcg_cmpxchg_lock(uintptr_t addr)
+{
+ assert(tcg_cmpxchg_curr_lock == NULL);
+ /* choose lock based on cache line address. We assume lines are 64b long */
+ addr >>= 6;
+ addr &= TCG_CMPXCHG_NR_LOCKS - 1;
+ tcg_cmpxchg_curr_lock = &tcg_cmpxchg_locks[addr];
+ qemu_mutex_lock(tcg_cmpxchg_curr_lock);
+}
+
+void tcg_cmpxchg_unlock(void)
+{
+ qemu_mutex_unlock(tcg_cmpxchg_curr_lock);
+ tcg_cmpxchg_curr_lock = NULL;
+}
+
+void tcg_cmpxchg_lock_reset(void)
+{
+ if (unlikely(tcg_cmpxchg_curr_lock)) {
+ tcg_cmpxchg_unlock();
+ }
+}
+
+void tcg_cmpxchg_lock_init(void)
+{
+ int i;
+
+ /* set current to NULL; useful after a child forks in user-mode */
+ tcg_cmpxchg_curr_lock = NULL;
+ for (i = 0; i < TCG_CMPXCHG_NR_LOCKS; i++) {
+ qemu_mutex_init(&tcg_cmpxchg_locks[i]);
+ }
+}
+
static TranslationBlock *tb_find_pc(uintptr_t tc_ptr);
void cpu_gen_init(void)
@@ -731,6 +769,7 @@ static inline void code_gen_alloc(size_t tb_size)
tcg_ctx.tb_ctx.tbs = g_new(TranslationBlock, tcg_ctx.code_gen_max_blocks);
qemu_mutex_init(&tcg_ctx.tb_ctx.tb_lock);
+ tcg_cmpxchg_lock_init();
}
static void tb_htable_init(void)
--
2.5.0
- [Qemu-devel] [RFC 00/30] cmpxchg-based emulation of atomics, Emilio G. Cota, 2016/06/27
- [Qemu-devel] [RFC 12/30] target-i386: emulate LOCK'ed OP instructions using atomic helpers, Emilio G. Cota, 2016/06/27
- [Qemu-devel] [RFC 09/30] softmmu: add atomic helpers, Emilio G. Cota, 2016/06/27
- [Qemu-devel] [RFC 07/30] atomics: add atomic_xor, Emilio G. Cota, 2016/06/27
- [Qemu-devel] [RFC 08/30] atomics: add atomic_op_fetch variants, Emilio G. Cota, 2016/06/27
- [Qemu-devel] [RFC 14/30] target-i386: emulate LOCK'ed NOT using atomic helper, Emilio G. Cota, 2016/06/27
- [Qemu-devel] [RFC 10/30] cpu_ldst: add cpu_atomic helpers, Emilio G. Cota, 2016/06/27
- [Qemu-devel] [RFC 11/30] target-i386: add atomic helpers, Emilio G. Cota, 2016/06/27