From 78722ed0b826644ae240e3c0bbb6bdde02dfe7e1 Mon Sep 17 00:00:00 2001 From: "Emilio G. Cota" Date: Wed, 26 Jul 2017 20:15:41 -0400 Subject: translate-all: make l1_map lockless MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Alex Bennée Signed-off-by: Emilio G. Cota Signed-off-by: Richard Henderson --- accel/tcg/translate-all.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) (limited to 'accel') diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c index 52e62125ed..52273e5846 100644 --- a/accel/tcg/translate-all.c +++ b/accel/tcg/translate-all.c @@ -469,20 +469,12 @@ static void page_init(void) #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) { PageDesc *pd; void **lp; int i; - if (alloc) { - assert_memory_lock(); - } - /* Level 1. Always allocated. */ 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); if (p == NULL) { + void *existing; + if (!alloc) { return NULL; } 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)); @@ -503,11 +501,17 @@ static PageDesc *page_find_alloc(tb_page_addr_t index, int alloc) pd = atomic_rcu_read(lp); if (pd == NULL) { + void *existing; + if (!alloc) { return NULL; } 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)); -- cgit v1.2.3