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Re: [Qemu-devel] [Qemu-ppc] [PATCH RFC v1 0/3] Enable MTTCG on PPC64

From: Alex Bennée
Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH RFC v1 0/3] Enable MTTCG on PPC64
Date: Mon, 10 Apr 2017 18:20:08 +0100
User-agent: mu4e 0.9.19; emacs 25.2.15

Cédric Le Goater <address@hidden> writes:

> On 04/07/2017 08:07 AM, Cédric Le Goater wrote:
>> On 04/07/2017 07:24 AM, Nikunj A Dadhania wrote:
>>> Cédric Le Goater <address@hidden> writes:
>>>> Hello Nikunj,
>>>> On 04/06/2017 12:22 PM, Nikunj A Dadhania wrote:
>>>>> The series enables Multi-Threaded TCG on PPC64
>>>>> Patch 01: Use atomic_cmpxchg in store conditional
>>>>>       02: Handle first write to page during atomic operation
>>>>>       03: Generate memory barriers for sync/isync and load/store 
>>>>> conditional
>>>>> Patches are based on ppc-for-2.10
>>>>> Tested using following:
>>>>> ./ppc64-softmmu/qemu-system-ppc64 -cpu POWER8 -vga none -nographic 
>>>>> -machine pseries,usb=off -m 2G  -smp 8,cores=8,threads=1 -accel 
>>>>> tcg,thread=multi  f23.img
>>>> I tried it with a Ubuntu 16.04.2 guest using stress --cpu 8. It looked
>>>> good : the CPU usage of QEMU reached 760% on the host.
>>> Cool.
>>>>> Todo:
>>>>> * Enable other machine types and PPC32.
>>>> I am quite ignorant on the topic.
>>>> Have you looked at what it would take to emulate support of the HW
>>>> threads ?
>>> We would need to implement msgsndp (doorbell support for IPI between
>>> threads of same core)
>> ok. I get it. Thanks,
>>>> and the PowerNV machine ?
>>> Haven't tried it, should work. Just give a shot, let me know if you see 
>>> problems.
>> sure. pnv is still on 2.9, so I will rebase on 2.10, merge your
>> patches  and tell you.
> The system seems to be spinning in skiboot in cpu_idle/relax when
> starting the linux kernel. It finally boots, but it is rather long.
> David has merged enough to test if you want to give it a try.

Does PPC have Wait-for-irq or similar "sleeping" instructions?

We had to ensure we were not jumping out of the cpu loop and suspend

See c22edfebff29f63d793032e4fbd42a035bb73e27 for an example.

Alex Bennée

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