From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35399) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1atXiv-000440-UN for qemu-devel@nongnu.org; Fri, 22 Apr 2016 05:50:07 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1atXiq-0003Db-PZ for qemu-devel@nongnu.org; Fri, 22 Apr 2016 05:50:05 -0400 Received: from mail-lf0-x233.google.com ([2a00:1450:4010:c07::233]:33775) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1atXiq-0003DB-6I for qemu-devel@nongnu.org; Fri, 22 Apr 2016 05:50:00 -0400 Received: by mail-lf0-x233.google.com with SMTP id e190so76185032lfe.0 for ; Fri, 22 Apr 2016 02:49:59 -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> <57190B52.7070409@gmail.com> <87r3dytyou.fsf@linaro.org> From: Sergey Fedorov Message-ID: <5719F3C5.90308@gmail.com> Date: Fri, 22 Apr 2016 12:49:57 +0300 MIME-Version: 1.0 In-Reply-To: <87r3dytyou.fsf@linaro.org> 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 22/04/16 00:54, Alex Bennée wrote: > Sergey Fedorov writes: > >> 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? > Yeah that sort of thing. Okay, I'll include this in the next respin. Kind regards, Sergey