From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:46832) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bLFFy-0002zS-SO for qemu-devel@nongnu.org; Thu, 07 Jul 2016 15:46:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bLFFu-0000yv-P2 for qemu-devel@nongnu.org; Thu, 07 Jul 2016 15:46:42 -0400 Received: from mail-lf0-x242.google.com ([2a00:1450:4010:c07::242]:34327) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bLFFu-0000yr-Al for qemu-devel@nongnu.org; Thu, 07 Jul 2016 15:46:38 -0400 Received: by mail-lf0-x242.google.com with SMTP id a10so567405lfb.1 for ; Thu, 07 Jul 2016 12:46:38 -0700 (PDT) References: <1467735496-16256-7-git-send-email-alex.bennee@linaro.org> <1467909880-18834-1-git-send-email-sergey.fedorov@linaro.org> <1467909880-18834-4-git-send-email-sergey.fedorov@linaro.org> <877fcxmeai.fsf@linaro.org> From: Sergey Fedorov Message-ID: <577EB19A.8040206@gmail.com> Date: Thu, 7 Jul 2016 22:46:34 +0300 MIME-Version: 1.0 In-Reply-To: <877fcxmeai.fsf@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH 3/3] tcg: Avoid bouncing tb_lock between tb_gen_code() and tb_add_jump() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Alex_Benn=c3=a9e?= , Sergey Fedorov Cc: qemu-devel@nongnu.org, patches@linaro.org, mttcg@listserver.greensocs.com, fred.konrad@greensocs.com, a.rigo@virtualopensystems.com, cota@braap.org, bobby.prani@gmail.com, rth@twiddle.net, 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 22:36, Alex Bennée wrote: > Sergey Fedorov writes: > >> From: Sergey Fedorov >> >> Signed-off-by: Sergey Fedorov >> Signed-off-by: Sergey Fedorov >> --- >> cpu-exec.c | 15 +++++++++------ >> 1 file changed, 9 insertions(+), 6 deletions(-) >> >> diff --git a/cpu-exec.c b/cpu-exec.c >> index dd0bd5007701..54c935039592 100644 >> --- a/cpu-exec.c >> +++ b/cpu-exec.c >> @@ -295,7 +295,8 @@ static TranslationBlock *tb_find_slow(CPUState *cpu, >> >> /* 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. >> + * single threaded the locks are NOPs. Both locks are to be >> + * released at the end of tb_find_fast(). >> */ >> mmap_lock(); >> tb_lock(); >> @@ -308,9 +309,6 @@ static TranslationBlock *tb_find_slow(CPUState *cpu, >> /* if no translated code available, then translate it now */ >> tb = tb_gen_code(cpu, pc, cs_base, flags, 0); >> } >> - >> - tb_unlock(); >> - mmap_unlock(); > Hmm pushing these outside of tb_find_slow() makes me uncomfortable. I > guess tb_find_fast/slow are intimately tied together but the idea of > taking locks which are the responsibility of the calling function to > clear seems ugly to me. Okay, what if we also: diff --git a/cpu-exec.c b/cpu-exec.c index 54c935039592..ff8f92bc1dc1 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -278,45 +278,7 @@ static TranslationBlock *tb_find_physical(CPUState *cpu, return qht_lookup(&tcg_ctx.tb_ctx.htable, tb_cmp, &desc, h); } -static TranslationBlock *tb_find_slow(CPUState *cpu, - target_ulong pc, - target_ulong cs_base, - uint32_t flags) -{ - TranslationBlock *tb; - - /* Ensure that we won't find a TB in the shared hash table - * if it is being invalidated by some other thread. - * Otherwise we'd put it back to CPU's local cache. - * Pairs with smp_wmb() in tb_phys_invalidate(). */ - smp_rmb(); - tb = tb_find_physical(cpu, pc, cs_base, flags); - if (!tb) { - - /* 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. Both locks are to be - * released at the end of tb_find_fast(). - */ - mmap_lock(); - tb_lock(); - - /* 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); - } - } - - /* 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; -} - -static inline TranslationBlock *tb_find_fast(CPUState *cpu, +static inline TranslationBlock *tb_find(CPUState *cpu, TranslationBlock **last_tb, int tb_exit) { @@ -332,7 +294,34 @@ static inline TranslationBlock *tb_find_fast(CPUState *cpu, 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)) { - tb = tb_find_slow(cpu, pc, cs_base, flags); + /* Ensure that we won't find a TB in the shared hash table + * if it is being invalidated by some other thread. + * Otherwise we'd put it back to CPU's local cache. + * Pairs with smp_wmb() in tb_phys_invalidate(). */ + smp_rmb(); + tb = tb_find_physical(cpu, pc, cs_base, flags); + if (!tb) { + + /* 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. Both locks are to be + * released at the end of the function. + */ + mmap_lock(); + tb_lock(); + + /* 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); + } + } + + /* 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); } if (cpu->tb_flushed) { /* Ensure that no TB jump will be modified as the @@ -440,7 +429,7 @@ static inline bool cpu_handle_exception(CPUState *cpu, int *ret) && cpu->icount_decr.u16.low + cpu->icount_extra == 0) { /* try to cause an exception pending in the log */ TranslationBlock *last_tb = NULL; /* Avoid chaining TBs */ - cpu_exec_nocache(cpu, 1, tb_find_fast(cpu, &last_tb, 0), true); + cpu_exec_nocache(cpu, 1, tb_find(cpu, &last_tb, 0), true); *ret = -1; return true; #endif @@ -624,7 +613,7 @@ int cpu_exec(CPUState *cpu) cpu->tb_flushed = false; /* reset before first TB lookup */ for(;;) { cpu_handle_interrupt(cpu, &last_tb); - tb = tb_find_fast(cpu, &last_tb, tb_exit); + tb = tb_find(cpu, &last_tb, tb_exit); cpu_loop_exec_tb(cpu, tb, &last_tb, &tb_exit, &sc); /* Try to align the host and virtual clocks if the guest is in advance */ Kind regards, Sergey > >> } >> >> /* We add the TB in the virtual pc hash table for the fast lookup */ >> @@ -354,10 +352,15 @@ 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(); >> + if (!tb_lock_locked()) { >> + tb_lock(); >> + } >> tb_add_jump(*last_tb, tb_exit, tb); >> - tb_unlock(); >> } >> + >> + tb_lock_reset(); >> + mmap_lock_reset(); >> + >> return tb; >> } > > -- > Alex Bennée