From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:33517) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dLEt8-0007Ea-60 for qemu-devel@nongnu.org; Wed, 14 Jun 2017 16:27:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dLEt4-0004e9-7L for qemu-devel@nongnu.org; Wed, 14 Jun 2017 16:27:38 -0400 Received: from out4-smtp.messagingengine.com ([66.111.4.28]:40741) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dLEt4-0004dq-0j for qemu-devel@nongnu.org; Wed, 14 Jun 2017 16:27:34 -0400 Date: Wed, 14 Jun 2017 16:27:33 -0400 From: "Emilio G. Cota" Message-ID: <20170614202733.GA8420@flamenco> References: <20170614194821.8754-1-rth@twiddle.net> <20170614194821.8754-2-rth@twiddle.net> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20170614194821.8754-2-rth@twiddle.net> Subject: [Qemu-devel] [PATCH] tcg-runtime: increase hit rate of lookup_tb_ptr List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Richard Henderson Cc: qemu-devel@nongnu.org, alex.bennee@linaro.org, pbonzini@redhat.com On Wed, Jun 14, 2017 at 12:48:17 -0700, Richard Henderson wrote: > 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. > > Signed-off-by: Richard Henderson I just wrote this alternative patch, which does the same thing as yours. I also measured what the effect of this change has on the hit rate of lookup_tb_ptr. Feel free to reuse parts of the patch and/or the commit message! Thanks, E. --- 8< --- Strangely, we do not look up the tb in the global hash table when we get NULL from tb_jmp_cache. Fix it, which improves the hit rate of lookup_tb_ptr; for instance, when booting and immediately shutting down debian-arm, the hit rate improves from 93.150742% (before this patch) to 99.451323 % (after). While at it, use a variable for the tb_jmp_cache hash and get rid of the goto's. Suggested-by: Richard Henderson Suggested-by: Alex Bennée Signed-off-by: Emilio G. Cota --- tcg-runtime.c | 20 ++++++++------------ 1 file changed, 8 insertions(+), 12 deletions(-) diff --git a/tcg-runtime.c b/tcg-runtime.c index 7fa90ce..09324b9 100644 --- a/tcg-runtime.c +++ b/tcg-runtime.c @@ -149,23 +149,19 @@ void *HELPER(lookup_tb_ptr)(CPUArchState *env, target_ulong addr) CPUState *cpu = ENV_GET_CPU(env); TranslationBlock *tb; target_ulong cs_base, pc; + unsigned int hash = tb_jmp_cache_hash_func(addr); uint32_t flags; - 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; - } + tb = atomic_rcu_read(&cpu->tb_jmp_cache[hash]); + cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags); + if (unlikely(tb == NULL || 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 (unlikely(tb == NULL)) { + return tcg_ctx.code_gen_epilogue; } + atomic_set(&cpu->tb_jmp_cache[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, -- 2.7.4