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translate-all: make l1_map lockless 

Groundwork for supporting parallel TCG generation.

We never remove entries from the radix tree, so we can use cmpxchg
to implement lockless insertions.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
This commit is contained in:
Emilio G. Cota 2017-07-26 20:15:41 -04:00 committed by Richard Henderson
parent 1e05197f24
commit 78722ed0b8
2 changed files with 16 additions and 12 deletions
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24
accel/tcg/translate-all.c
View File

@ -469,20 +469,12 @@ static void page_init(void)
#endif #endif
} }
/* If alloc=1:
* Called with tb_lock held for system emulation.
* Called with mmap_lock held for user-mode emulation.
*/
static PageDesc *page_find_alloc(tb_page_addr_t index, int alloc) static PageDesc *page_find_alloc(tb_page_addr_t index, int alloc)
{ {
PageDesc *pd; PageDesc *pd;
void **lp; void **lp;
int i; int i;
if (alloc) {
assert_memory_lock();
}
/* Level 1. Always allocated. */ /* Level 1. Always allocated. */
lp = l1_map + ((index >> v_l1_shift) & (v_l1_size - 1)); lp = l1_map + ((index >> v_l1_shift) & (v_l1_size - 1));
@ -491,11 +483,17 @@ static PageDesc *page_find_alloc(tb_page_addr_t index, int alloc)
void **p = atomic_rcu_read(lp); void **p = atomic_rcu_read(lp);
if (p == NULL) { if (p == NULL) {
void *existing;
if (!alloc) { if (!alloc) {
return NULL; return NULL;
} }
p = g_new0(void *, V_L2_SIZE); p = g_new0(void *, V_L2_SIZE);
atomic_rcu_set(lp, p); existing = atomic_cmpxchg(lp, NULL, p);
if (unlikely(existing)) {
g_free(p);
p = existing;
}
} }
lp = p + ((index >> (i * V_L2_BITS)) & (V_L2_SIZE - 1)); lp = p + ((index >> (i * V_L2_BITS)) & (V_L2_SIZE - 1));
@ -503,11 +501,17 @@ static PageDesc *page_find_alloc(tb_page_addr_t index, int alloc)
pd = atomic_rcu_read(lp); pd = atomic_rcu_read(lp);
if (pd == NULL) { if (pd == NULL) {
void *existing;
if (!alloc) { if (!alloc) {
return NULL; return NULL;
} }
pd = g_new0(PageDesc, V_L2_SIZE); pd = g_new0(PageDesc, V_L2_SIZE);
atomic_rcu_set(lp, pd); existing = atomic_cmpxchg(lp, NULL, pd);
if (unlikely(existing)) {
g_free(pd);
pd = existing;
}
} }
return pd + (index & (V_L2_SIZE - 1)); return pd + (index & (V_L2_SIZE - 1));

4
docs/devel/multi-thread-tcg.txt
View File

@ -134,8 +134,8 @@ tb_set_jmp_target() code. Modification to the linked lists that allow
searching for linked pages are done under the protect of the searching for linked pages are done under the protect of the
tb_lock(). tb_lock().
The global page table is protected by the tb_lock() in system-mode and The global page table is a lockless radix tree; cmpxchg is used
mmap_lock() in linux-user mode. to atomically insert new elements.
The lookup caches are updated atomically and the lookup hash uses QHT The lookup caches are updated atomically and the lookup hash uses QHT
which is designed for concurrent safe lookup. which is designed for concurrent safe lookup.