From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46434) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bLY37-0008Kk-6J for qemu-devel@nongnu.org; Fri, 08 Jul 2016 11:50:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bLY33-000614-2M for qemu-devel@nongnu.org; Fri, 08 Jul 2016 11:50:40 -0400 Received: from mail-lf0-x241.google.com ([2a00:1450:4010:c07::241]:34609) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bLY32-00060K-HD for qemu-devel@nongnu.org; Fri, 08 Jul 2016 11:50:36 -0400 Received: by mail-lf0-x241.google.com with SMTP id a10so6336021lfb.1 for ; Fri, 08 Jul 2016 08:50:36 -0700 (PDT) References: <1467735496-16256-1-git-send-email-alex.bennee@linaro.org> <1467735496-16256-4-git-send-email-alex.bennee@linaro.org> <577E64BC.4070505@gmail.com> From: Sergey Fedorov Message-ID: <577FCBC9.4010504@gmail.com> Date: Fri, 8 Jul 2016 18:50:33 +0300 MIME-Version: 1.0 In-Reply-To: <577E64BC.4070505@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH v2 3/6] tcg: cpu-exec: remove tb_lock from the hot-path List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Alex_Benn=c3=a9e?= , mttcg@listserver.greensocs.com, qemu-devel@nongnu.org, fred.konrad@greensocs.com, a.rigo@virtualopensystems.com, cota@braap.org, bobby.prani@gmail.com, rth@twiddle.net Cc: mark.burton@greensocs.com, pbonzini@redhat.com, jan.kiszka@siemens.com, peter.maydell@linaro.org, claudio.fontana@huawei.com, Peter Crosthwaite On 07/07/16 17:18, Sergey Fedorov wrote: > On 05/07/16 19:18, Alex Bennée wrote: >> Lock contention in the hot path of moving between existing patched >> TranslationBlocks is the main drag in multithreaded performance. This >> patch pushes the tb_lock() usage down to the two places that really need >> it: >> >> - code generation (tb_gen_code) >> - jump patching (tb_add_jump) >> >> The rest of the code doesn't really need to hold a lock as it is either >> using per-CPU structures, atomically updated or designed to be used in >> concurrent read situations (qht_lookup). >> >> To keep things simple I removed the #ifdef CONFIG_USER_ONLY stuff as the >> locks become NOPs anyway until the MTTCG work is completed. >> >> Signed-off-by: Alex Bennée >> Reviewed-by: Richard Henderson > Reviewed-by: Sergey Fedorov Revoked: CPUState::tb_flushed must also be protected by tb_lock. > >> --- >> v3 (base-patches) >> - fix merge conflicts with Sergey's patch >> v1 (hot path, split from base-patches series) >> - revert name tweaking >> - drop test jmp_list_next outside lock >> - mention lock NOPs in comments >> v2 (hot path) >> - Add r-b tags >> --- >> cpu-exec.c | 48 +++++++++++++++++++++--------------------------- >> 1 file changed, 21 insertions(+), 27 deletions(-) >> >> diff --git a/cpu-exec.c b/cpu-exec.c >> index 10ce1cb..dd0bd50 100644 >> --- a/cpu-exec.c >> +++ b/cpu-exec.c >> @@ -291,35 +291,29 @@ static TranslationBlock *tb_find_slow(CPUState *cpu, >> * Pairs with smp_wmb() in tb_phys_invalidate(). */ >> smp_rmb(); >> tb = tb_find_physical(cpu, pc, cs_base, flags); >> - if (tb) { >> - goto found; >> - } >> + if (!tb) { >> >> -#ifdef CONFIG_USER_ONLY >> - /* mmap_lock is needed by tb_gen_code, and mmap_lock must be >> - * taken outside tb_lock. Since we're momentarily dropping >> - * tb_lock, there's a chance that our desired tb has been >> - * translated. >> - */ >> - tb_unlock(); >> - mmap_lock(); >> - tb_lock(); >> - tb = tb_find_physical(cpu, pc, cs_base, flags); >> - if (tb) { >> - mmap_unlock(); >> - goto found; >> - } >> -#endif >> + /* mmap_lock is needed by tb_gen_code, and mmap_lock must be >> + * taken outside tb_lock. As system emulation is currently >> + * single threaded the locks are NOPs. >> + */ >> + mmap_lock(); >> + tb_lock(); >> >> - /* if no translated code available, then translate it now */ >> - tb = tb_gen_code(cpu, pc, cs_base, flags, 0); >> + /* There's a chance that our desired tb has been translated while >> + * taking the locks so we check again inside the lock. >> + */ >> + tb = tb_find_physical(cpu, pc, cs_base, flags); >> + if (!tb) { >> + /* if no translated code available, then translate it now */ >> + tb = tb_gen_code(cpu, pc, cs_base, flags, 0); >> + } >> >> -#ifdef CONFIG_USER_ONLY >> - mmap_unlock(); >> -#endif >> + tb_unlock(); >> + mmap_unlock(); >> + } >> >> -found: >> - /* we add the TB in the virtual pc hash table */ >> + /* We add the TB in the virtual pc hash table for the fast lookup */ >> atomic_set(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)], tb); >> return tb; >> } >> @@ -337,7 +331,6 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu, >> always be the same before a given translated block >> is executed. */ >> cpu_get_tb_cpu_state(env, &pc, &cs_base, &flags); >> - tb_lock(); >> tb = atomic_read(&cpu->tb_jmp_cache[tb_jmp_cache_hash_func(pc)]); >> if (unlikely(!tb || tb->pc != pc || tb->cs_base != cs_base || >> tb->flags != flags)) { >> @@ -361,9 +354,10 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu, >> #endif >> /* See if we can patch the calling TB. */ >> if (*last_tb && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) { >> + tb_lock(); >> tb_add_jump(*last_tb, tb_exit, tb); >> + tb_unlock(); >> } >> - tb_unlock(); >> return tb; >> } >>