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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%.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
Signed-off-by: Richard Henderson <rth@twiddle.net>
This commit is contained in:
Richard Henderson 2017-06-14 08:18:36 -07:00
parent 308714e6bc
commit b97a879de9
1 changed files with 13 additions and 13 deletions
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26
tcg-runtime.c
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@ -149,23 +149,23 @@ 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)) {
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;
}
addr_hash = tb_jmp_cache_hash_func(addr);
tb = atomic_rcu_read(&cpu->tb_jmp_cache[addr_hash]);
cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags);
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;
}
atomic_set(&cpu->tb_jmp_cache[addr_hash], tb);
}
return tcg_ctx.code_gen_epilogue;
found:
qemu_log_mask_and_addr(CPU_LOG_EXEC, addr,
"Chain %p [%d: " TARGET_FMT_lx "] %s\n",
tb->tc_ptr, cpu->cpu_index, addr,