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translate-all: discard TB when tb_link_page returns an existing matching TB

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Use the recently-gained QHT feature of returning the matching TB if it
already exists. This allows us to get rid of the lookup we perform
right after acquiring tb_lock.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@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 2017-08-01 15:40:16 -04:00 • committed by Richard Henderson
parent faa9372c07
commit 95590e24af
3 changed files with 46 additions and 21 deletions
Download patch file Download diff file Expand all files Collapse all files

14
accel/tcg/cpu-exec.c
View file

@ -245,10 +245,7 @@ void cpu_exec_step_atomic(CPUState *cpu)
if (tb == NULL) {
mmap_lock();
tb_lock();
tb = tb_htable_lookup(cpu, pc, cs_base, flags, cf_mask);
if (likely(tb == NULL)) {
tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
}
tb = tb_gen_code(cpu, pc, cs_base, flags, cflags);
tb_unlock();
mmap_unlock();
}
@ -398,14 +395,7 @@ static inline TranslationBlock *tb_find(CPUState *cpu,
tb_lock();
acquired_tb_lock = true;
/* There's a chance that our desired tb has been translated while
* taking the locks so we check again inside the lock.
*/
tb = tb_htable_lookup(cpu, pc, cs_base, flags, cf_mask);
if (likely(tb == NULL)) {
/* if no translated code available, then translate it now */
tb = tb_gen_code(cpu, pc, cs_base, flags, cf_mask);
}
tb = tb_gen_code(cpu, pc, cs_base, flags, cf_mask);
mmap_unlock();
/* We add the TB in the virtual pc hash table for the fast lookup */

50
accel/tcg/translate-all.c
View file

@ -1581,18 +1581,30 @@ static inline void tb_page_add(PageDesc *p, TranslationBlock *tb,
* (-1) to indicate that only one page contains the TB.
*
* Called with mmap_lock held for user-mode emulation.
*
* Returns a pointer @tb, or a pointer to an existing TB that matches @tb.
* Note that in !user-mode, another thread might have already added a TB
* for the same block of guest code that @tb corresponds to. In that case,
* the caller should discard the original @tb, and use instead the returned TB.
*/
static void tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
tb_page_addr_t phys_page2)
static TranslationBlock *
tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
tb_page_addr_t phys_page2)
{
PageDesc *p;
PageDesc *p2 = NULL;
void *existing_tb = NULL;
uint32_t h;
assert_memory_lock();
/*
* Add the TB to the page list, acquiring first the pages's locks.
* We keep the locks held until after inserting the TB in the hash table,
* so that if the insertion fails we know for sure that the TBs are still
* in the page descriptors.
* Note that inserting into the hash table first isn't an option, since
* we can only insert TBs that are fully initialized.
*/
page_lock_pair(&p, phys_pc, &p2, phys_page2, 1);
tb_page_add(p, tb, 0, phys_pc & TARGET_PAGE_MASK);
@ -1602,21 +1614,33 @@ static void tb_link_page(TranslationBlock *tb, tb_page_addr_t phys_pc,
tb->page_addr[1] = -1;
}
/* add in the hash table */
h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->cflags & CF_HASH_MASK,
tb->trace_vcpu_dstate);
qht_insert(&tb_ctx.htable, tb, h, &existing_tb);
/* remove TB from the page(s) if we couldn't insert it */
if (unlikely(existing_tb)) {
tb_page_remove(p, tb);
invalidate_page_bitmap(p);
if (p2) {
tb_page_remove(p2, tb);
invalidate_page_bitmap(p2);
}
tb = existing_tb;
}
if (p2) {
page_unlock(p2);
}
page_unlock(p);
/* add in the hash table */
h = tb_hash_func(phys_pc, tb->pc, tb->flags, tb->cflags & CF_HASH_MASK,
tb->trace_vcpu_dstate);
qht_insert(&tb_ctx.htable, tb, h, NULL);
#ifdef CONFIG_USER_ONLY
if (DEBUG_TB_CHECK_GATE) {
tb_page_check();
}
#endif
return tb;
}
/* Called with mmap_lock held for user mode emulation. */
@ -1625,7 +1649,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
uint32_t flags, int cflags)
{
CPUArchState *env = cpu->env_ptr;
TranslationBlock *tb;
TranslationBlock *tb, *existing_tb;
tb_page_addr_t phys_pc, phys_page2;
target_ulong virt_page2;
tcg_insn_unit *gen_code_buf;
@ -1773,7 +1797,15 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
* memory barrier is required before tb_link_page() makes the TB visible
* through the physical hash table and physical page list.
*/
tb_link_page(tb, phys_pc, phys_page2);
existing_tb = tb_link_page(tb, phys_pc, phys_page2);
/* if the TB already exists, discard what we just translated */
if (unlikely(existing_tb != tb)) {
uintptr_t orig_aligned = (uintptr_t)gen_code_buf;
orig_aligned -= ROUND_UP(sizeof(*tb), qemu_icache_linesize);
atomic_set(&tcg_ctx->code_gen_ptr, (void *)orig_aligned);
return existing_tb;
}
tcg_tb_insert(tb);
return tb;
}