Commit 78722ed0 authored by Emilio G. Cota's avatar Emilio G. Cota Committed by Richard Henderson
Browse files

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: default avatarRichard Henderson <richard.henderson@linaro.org>
Reviewed-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: default avatarEmilio G. Cota <cota@braap.org>
Signed-off-by: default avatarRichard Henderson <richard.henderson@linaro.org>
parent 1e05197f

accel/tcg/translate-all.c

+14 −10
Original line number Diff line number Diff line
@@ -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));

docs/devel/multi-thread-tcg.txt

+2 −2
Original line number Diff line number Diff line
@@ -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

tb_lock().



The global page table is protected by the tb_lock() in system-mode and

mmap_lock() in linux-user mode.

The global page table is a lockless radix tree; cmpxchg is used

to atomically insert new elements.



The lookup caches are updated atomically and the lookup hash uses QHT

which is designed for concurrent safe lookup.