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tcg: Increase hit rate of lookup_tb_ptr

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We can call tb_htable_lookup even when the tb_jmp_cache is completely
empty. Therefore, un-nest most of the code dependent on tb != NULL
from the read from the cache.

This improves the hit rate of lookup_tb_ptr; for instance, when booting
and immediately shutting down debian-arm, the hit rate improves from
93.2% to 99.4%.

Backports commit b97a879de980e99452063851597edb98e7e8039c from qemu
This commit is contained in:
Richard Henderson 2018-03-03 17:16:21 -05:00 committed by Lioncash
parent 9ec975448b
commit dd1473f582
No known key found for this signature in database
GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 14 additions and 13 deletions
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27
qemu/tcg-runtime.c
View file

@ -149,23 +149,24 @@ void *HELPER(lookup_tb_ptr)(CPUArchState *env, target_ulong addr)
CPUState *cpu = ENV_GET_CPU(env);
TranslationBlock *tb;
target_ulong cs_base, pc;
uint32_t flags;
uint32_t flags, addr_hash;
tb = atomic_rcu_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)]);
if (likely(tb)) {
addr_hash = tb_jmp_cache_hash_func(addr);
// Unicorn: atomic_read used instead of atomic_rcu_read
tb = atomic_read(&cpu->tb_jmp_cache[addr_hash]);
cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
if (likely(tb->pc == addr && tb->cs_base == cs_base &&
tb->flags == flags)) {
goto found;
}
if (unlikely(!(tb
&& tb->pc == addr
&& tb->cs_base == cs_base
&& tb->flags == flags))) {
tb = tb_htable_lookup(cpu, addr, cs_base, flags);
if (likely(tb)) {
atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(addr)], tb);
goto found;
}
}
if (!tb) {
return tcg_ctx->code_gen_epilogue;
found:
}
atomic_set(&cpu->tb_jmp_cache[addr_hash], tb);
}
// Unicorn: commented out
//qemu_log_mask_and_addr(CPU_LOG_EXEC, addr,
// "Chain %p [%d: " TARGET_FMT_lx "] %s\n",