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Date: Mon, 20 Dec 2010 10:25:15 +0100
From: Fabien Chouteau <chouteau@adacore.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH 5/6] [RFC] Emulation of Leon3.
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: qemu-devel@nongnu.org

On 12/17/2010 08:14 PM, Blue Swirl wrote:
> On Wed, Dec 15, 2010 at 5:47 PM, Fabien Chouteau<chouteau@adacore.com>  wrote:
>> On 12/13/2010 07:18 PM, Blue Swirl wrote:
>>>
>>> On Mon, Dec 13, 2010 at 3:51 PM, Fabien Chouteau<chouteau@adacore.com>
>>>   wrote:
>>>>
>>>> On 12/11/2010 10:56 AM, Blue Swirl wrote:
>>>>>
>>>>> On Tue, Dec 7, 2010 at 11:40 AM, Fabien Chouteau<chouteau@adacore.com>
>>>>>   wrote:
>>>>>>
>>>>>> On 12/06/2010 06:53 PM, Blue Swirl wrote:
>>>>>>>
>>>>>>> On Mon, Dec 6, 2010 at 9:26 AM, Fabien Chouteau<chouteau@adacore.com>
>>>>>>>   wrote:
>>>>>>>
>>>>>>>> +#if !defined(CONFIG_USER_ONLY)
>>>>>>>> +    /* Leon3 shutdown */
>>>>>>>> +    if (intno == 0x80&&        env->version == 0xf3000000) {
>>>>>>>> +        leon3_shutdown();
>>>>>>>> +    }
>>>>>>>
>>>>>>> This looks like a hack. Should a trap instruction initiate a shutdown?
>>>>>>
>>>>>> Yes, on Leon3 "ta 0x0" initiates a shutdown.
>>>>>
>>>>> Then this should be handled during translation. A Leon3 specific CPU
>>>>> feature should be added and used much like CHECK_IU_FEATURE (in
>>>>> translate.c). Then execution speed would not be affected for non-Leon3
>>>>> CPUs.
>>>>>
>>>>
>>>> OK, but I don't see how to request a shutdown during translation.
>>>
>>> Just create a helper which calls shutdown, translator should insert a
>>> call to that.
>>
>> I think I understand what you mean, but I don't see why this would be faster
>> than my solution.
>
> Shutdown is not performance critical, but interrupt handling is.
>

I understand that, but why is it faster to do it during translation?

I don't see how one "if" statement in "do_interrupt" will even slightly 
impact
the performances, and why it will be slower than the same "if' statement 
in the translation.

BTW, I didn't use the "unlikely" function, but this will even more 
reduce the impact...

-- 
Fabien Chouteau