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author | Emilio G. Cota <cota@braap.org> | 2017-08-01 15:40:16 -0400 |
---|---|---|
committer | Richard Henderson <richard.henderson@linaro.org> | 2018-06-15 08:18:42 -1000 |
commit | 95590e24af11236ef334f6bc3e2b71404a790ddb (patch) | |
tree | 76e03c0f097bd05f4921fdc6cbe067cc9e2e598e /accel | |
parent | faa9372c07d062eb01f9da72e3f6c0f32efffca7 (diff) | |
download | qemu-95590e24af11236ef334f6bc3e2b71404a790ddb.zip qemu-95590e24af11236ef334f6bc3e2b71404a790ddb.tar.gz qemu-95590e24af11236ef334f6bc3e2b71404a790ddb.tar.bz2 |
translate-all: discard TB when tb_link_page returns an existing matching TB
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>
Diffstat (limited to 'accel')
-rw-r--r-- | accel/tcg/cpu-exec.c | 14 | ||||
-rw-r--r-- | accel/tcg/translate-all.c | 50 |
2 files changed, 43 insertions, 21 deletions
diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c index d75c353..45f6ebc 100644 --- a/accel/tcg/cpu-exec.c +++ b/accel/tcg/cpu-exec.c @@ -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 */ diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c index c75298d..3f97753 100644 --- a/accel/tcg/translate-all.c +++ b/accel/tcg/translate-all.c @@ -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; } |