From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:45945) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1atIF9-0008OV-8g for qemu-devel@nongnu.org; Thu, 21 Apr 2016 13:18:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1atIF4-0002oB-69 for qemu-devel@nongnu.org; Thu, 21 Apr 2016 13:18:19 -0400 Received: from mail-lb0-x22e.google.com ([2a00:1450:4010:c04::22e]:34230) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1atIF3-0002o6-KM for qemu-devel@nongnu.org; Thu, 21 Apr 2016 13:18:14 -0400 Received: by mail-lb0-x22e.google.com with SMTP id b1so27181854lbi.1 for ; Thu, 21 Apr 2016 10:18:13 -0700 (PDT) References: <1460666749-24452-1-git-send-email-sergey.fedorov@linaro.org> <1460666749-24452-5-git-send-email-sergey.fedorov@linaro.org> <87inzfvwiq.fsf@linaro.org> <5714F7C4.6040306@gmail.com> <87h9eyx2e9.fsf@linaro.org> <57151EA4.7040309@gmail.com> <5718E54B.1020602@gmail.com> <87twivt0qo.fsf@linaro.org> <5718FCE1.4050106@gmail.com> From: Sergey Fedorov Message-ID: <57190B52.7070409@gmail.com> Date: Thu, 21 Apr 2016 20:18:10 +0300 MIME-Version: 1.0 In-Reply-To: <5718FCE1.4050106@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?UTF-8?Q?Alex_Benn=c3=a9e?= Cc: Sergey Fedorov , qemu-devel@nongnu.org, Paolo Bonzini , Peter Crosthwaite , Richard Henderson , =?UTF-8?Q?Andreas_F=c3=a4rber?= On 21/04/16 19:16, Sergey Fedorov wrote: > On 21/04/16 18:55, Alex Bennée wrote: >> Sergey Fedorov writes: >> >>> On 18/04/16 20:51, Sergey Fedorov wrote: >>>> On 18/04/16 20:17, Alex Bennée wrote: >>>>> Sergey Fedorov writes: >>>>>> On 18/04/16 17:09, Alex Bennée wrote: >>>>>>> Sergey Fedorov writes: >>>>>>>> diff --git a/cpu-exec.c b/cpu-exec.c >>>>>> (snip) >>>>>>>> @@ -507,14 +510,12 @@ int cpu_exec(CPUState *cpu) >>>>>>>> } >>>>>>>> tb_lock(); >>>>>>>> tb = tb_find_fast(cpu); >>>>>>>> - /* Note: we do it here to avoid a gcc bug on Mac OS X when >>>>>>>> - doing it in tb_find_slow */ >>>>>>> Is this still true? Would it make more sense to push the patching down >>>>>>> to the gen_code? >>>>>> This comment comes up to the commit: >>>>>> >>>>>> commit 1538800276aa7228d74f9d00bf275f54dc9e9b43 >>>>>> Author: bellard >>>>>> Date: Mon Dec 19 01:42:32 2005 +0000 >>>>>> >>>>>> workaround for gcc bug on PowerPC >>>>>> >>>>>> >>>>>> It was added more than ten years ago. Anyway, now this code is here not >>>>>> because of the bug: we need to reset 'next_tb' which is a local variable >>>>>> in cpu_exec(). Personally, I don't think it would be neater to hide it >>>>>> into gen_code(). Do you have some thoughts on how we could benefit from >>>>>> doing so? BTW, I had a feeling that it may be useful to reorganize >>>>>> cpu_exec() a bit, although I don't have a solid idea of how to do this >>>>>> so far. >>>>> I'm mainly eyeing the tb_lock/unlock which would be nice to push further >>>>> down the call chain if we can, especially if the need to lock >>>>> tb_find_fast can be removed later on. >>>> Yes, it would be nice to possibly have all tb_lock/unlock() calls (or at >>>> least their pairs) in the same block. There is a lot to be thought over :) >>> It's not so simple because tb_find_fast() is also called in replay mode >>> to find a TB for cpu_exec_nocache()... I'm not sure it's worth touching >>> it now. >> If the locking is pushed into tb_find_fast or further down is this an >> issue? > We would have to pass 'next_tb' (or 'last_tb' and 'tb_exit' after > cleaning it up) if we move TB chaining code to tb_find_fast(). But > tb_find_fast() is also called in replay mode to find a TB for > cpu_exec_nocache() where we don't bother with TB chaining... Do you > think it would be fine to make those changes? Are you thinking about something like this: diff --git a/cpu-exec.c b/cpu-exec.c index 1d12e8bc2739..07e9ede49193 100644 --- a/cpu-exec.c +++ b/cpu-exec.c @@ -320,7 +320,9 @@ found: return tb; } -static inline TranslationBlock *tb_find_fast(CPUState *cpu) +static inline TranslationBlock *tb_find_fast(CPUState *cpu, + TranslationBlock **last_tb, + int tb_exit) { CPUArchState *env = (CPUArchState *)cpu->env_ptr; TranslationBlock *tb; @@ -331,11 +333,27 @@ 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 = 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); } + if (cpu->tb_flushed) { + /* Ensure that no TB jump will be modified as the + * translation buffer has been flushed. + */ + *last_tb = NULL; + cpu->tb_flushed = false; + } + /* see if we can patch the calling TB. When the TB + spans two pages, we cannot safely do a direct + jump. */ + if (*last_tb != NULL && tb->page_addr[1] == -1 + && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) { + tb_add_jump(*last_tb, tb_exit, tb); + } + tb_unlock(); return tb; } @@ -441,7 +459,8 @@ int cpu_exec(CPUState *cpu) } else if (replay_has_exception() && cpu->icount_decr.u16.low + cpu->icount_extra == 0) { /* try to cause an exception pending in the log */ - cpu_exec_nocache(cpu, 1, tb_find_fast(cpu), true); + last_tb = NULL; /* Avoid chaining TBs */ + cpu_exec_nocache(cpu, 1, tb_find_fast(cpu, &last_tb, 0), true); ret = -1; break; #endif @@ -511,23 +530,7 @@ int cpu_exec(CPUState *cpu) cpu->exception_index = EXCP_INTERRUPT; cpu_loop_exit(cpu); } - tb_lock(); - tb = tb_find_fast(cpu); - if (cpu->tb_flushed) { - /* Ensure that no TB jump will be modified as the - * translation buffer has been flushed. - */ - last_tb = NULL; - cpu->tb_flushed = false; - } - /* see if we can patch the calling TB. When the TB - spans two pages, we cannot safely do a direct - jump. */ - if (last_tb != NULL && tb->page_addr[1] == -1 - && !qemu_loglevel_mask(CPU_LOG_TB_NOCHAIN)) { - tb_add_jump(last_tb, tb_exit, tb); - } - tb_unlock(); + tb = tb_find_fast(cpu, &last_tb, tb_exit); if (likely(!cpu->exit_request)) { uintptr_t ret; trace_exec_tb(tb, tb->pc); ... right? Kind regards, Sergey