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Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag
From: |
Sergey Fedorov |
Subject: |
Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag |
Date: |
Thu, 21 Apr 2016 20:18:10 +0300 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 |
On 21/04/16 19:16, Sergey Fedorov wrote:
> On 21/04/16 18:55, Alex Bennée wrote:
>> Sergey Fedorov <address@hidden> writes:
>>
>>> On 18/04/16 20:51, Sergey Fedorov wrote:
>>>> On 18/04/16 20:17, Alex Bennée wrote:
>>>>> Sergey Fedorov <address@hidden> writes:
>>>>>> On 18/04/16 17:09, Alex Bennée wrote:
>>>>>>> Sergey Fedorov <address@hidden> 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 <address@hidden>
>>>>>> 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
- [Qemu-devel] [PATCH v3 3/4] cpu-exec: elide more icount code if CONFIG_USER_ONLY, (continued)
- [Qemu-devel] [PATCH v3 3/4] cpu-exec: elide more icount code if CONFIG_USER_ONLY, Sergey Fedorov, 2016/04/14
- [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Sergey Fedorov, 2016/04/14
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Alex Bennée, 2016/04/18
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Sergey Fedorov, 2016/04/18
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Peter Maydell, 2016/04/18
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Alex Bennée, 2016/04/18
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Sergey Fedorov, 2016/04/18
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Sergey Fedorov, 2016/04/21
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Alex Bennée, 2016/04/21
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Sergey Fedorov, 2016/04/21
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag,
Sergey Fedorov <=
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Alex Bennée, 2016/04/21
- Re: [Qemu-devel] [PATCH v3 4/4] tcg: rework tb_invalidated_flag, Sergey Fedorov, 2016/04/22