Re: [Qemu-ppc] [Qemu-devel] [PATCH RFC 0/4] Enable MTTCG on PowerPC

[Cédric Le Goater]

On 09/02/2016 09:57 AM, Thomas Huth wrote:
> On 02.09.2016 08:43, Cédric Le Goater wrote:
>> On 09/02/2016 08:32 AM, Nikunj A Dadhania wrote:
>>> The series is a first attempt at enabling Multi-Threaded TCG on PowerPC.
>>> Changes that were needed to enable PowerPC are pretty simple;
>>>
>>> Patch 01: Take a iothread lock during hcall, as hcall can generate io 
>>> requests
>>>       02: For TCG, we were harcoding smt as 1, this gets rid of the 
>>> limitation
>>>       03: Use atomic_cmpxchg in store conditional
>>>       04: With more threads, flush the entry from each cpu. 
>>>       This can be optimized further.
>>>
>>> The patches are based on the Alex Bennee's base enabling patches for 
>>> MTTCG[1] and Emilios's cmpxchg atomics. The consolidated tree of the 
>>> above patches is here:
>>>
>>> https://github.com/stsquad/qemu/tree/mttcg/base-patches-v4-with-cmpxchg-atomics-v2
>>>
>>> Apart from the above, PPC patches are based out of ppc-for-2.8 and 
>>> load/store consolidation patches [2]
>>>
>>> Series with all dependent patches available here: 
>>> https://github.com/nikunjad/qemu/tree/ppc_mttcg_v1
>>>
>>> Testing: 
>>> ========
>>>
>>> -smp 4,cores=1,threads=4 -accel tcg,thread=multi
>>>
>>> TODO
>>> ====
>>> Implement msgsndp instructions(door-bell), newer kernels enable it 
>>> depending on the PVR. I have been using following workaround to boot.
>>> https://github.com/nikunjad/qemu/commit/2c10052c5f93418a6b920e6ba3ce1813fcf50bc4
>>
>> You could also introduce a Power8 DD1 in qemu. From the kernel cputable :
>>
>>      {       /* Power8 DD1: Does not support doorbell IPIs */
>>              .pvr_mask               = 0xffffff00,
>>              .pvr_value              = 0x004d0100,
>>              .cpu_name               = "POWER8 (raw)",
>>              .cpu_features           = CPU_FTRS_POWER8_DD1,
>>              ...
> 
> Please try to avoid that! We just got rid of DD1 in qemu a couple of
> months ago:
> 
> http://git.qemu.org/?p=qemu.git;a=commitdiff;h=9d6ba75df26d699a6

he. I missed that. So the suggestion is a bit unfortunate. 

Thanks,
C.