From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:50308) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1atMYi-0004uh-Ke for qemu-devel@nongnu.org; Thu, 21 Apr 2016 17:54:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1atMYf-0004s9-Ce for qemu-devel@nongnu.org; Thu, 21 Apr 2016 17:54:48 -0400 Received: from mail-wm0-x22f.google.com ([2a00:1450:400c:c09::22f]:38698) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1atMYe-0004rY-U4 for qemu-devel@nongnu.org; Thu, 21 Apr 2016 17:54:45 -0400 Received: by mail-wm0-x22f.google.com with SMTP id u206so153058571wme.1 for ; Thu, 21 Apr 2016 14:54:44 -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> From: Alex =?utf-8?Q?Benn=C3=A9e?= In-reply-to: <57190B52.7070409@gmail.com> Date: Thu, 21 Apr 2016 22:54:41 +0100 Message-ID: <87r3dytyou.fsf@linaro.org> MIME-Version: 1.0 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: Sergey Fedorov Cc: Sergey Fedorov , qemu-devel@nongnu.org, Paolo Bonzini , Peter Crosthwaite , Richard Henderson , Andreas =?utf-8?Q?F=C3=A4rber?= 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. > > Kind regards, > Sergey -- Alex Bennée