Re: [EXTERNAL] Re: [PULL 18/23] accel/tcg: re-factor non-RAM execution code

[Cédric Le Goater]

On 4/15/21 5:55 PM, Philippe Mathieu-Daudé wrote:
> On 4/15/21 4:54 PM, Peter Maydell wrote:
>> On Thu, 15 Apr 2021 at 15:32, Alex Bennée <alex.bennee@linaro.org> wrote:
>>> --8<---------------cut here---------------start------------->8---
>>> accel/tcg: avoid re-translating one-shot instructions
>>>
>>> By definition a single instruction is capable of being an IO
>>> instruction. This avoids a problem of triggering a cpu_io_recompile on
>>> a non-cached translation which would only do exactly this anyway.
>>>
>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>>
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>> accel/tcg/translate-all.c | 2 +-
>>>
>>> modified   accel/tcg/translate-all.c
>>> @@ -1863,7 +1863,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
>>>
>>>      if (phys_pc == -1) {
>>>          /* Generate a one-shot TB with 1 insn in it */
>>> -        cflags = (cflags & ~CF_COUNT_MASK) | 1;
>>> +        cflags = (cflags & ~CF_COUNT_MASK) | CF_LAST_IO | 1;
>>>      }
>>>
>>>      max_insns = cflags & CF_COUNT_MASK;
>>> --8<---------------cut here---------------end--------------->8---
>>
>> Yes, this fixes the problem. Do we want to put this in for 6.0? My
>> feeling is that executing from non-RAM is pretty niche, so maybe
>> if we need an rc4 anyway, but this isn't important enough to cause an
>> rc4 itself.
> 
> Isn't it the default for Aspeed machines (with U-Boot)? (Cc'ing Cédric).

You need to set the 'execute-in-place' machine option to load/execute the
instructions from the AHB window of CE0. It's not on by default because 
boot can be really slow with some recent u-boot which heavily trash the TBs.

But this seems to work fine with -rc3. 

C.