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

From: "Cédric Le Goater" <clg@kaod.org>
To: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>,
	qemu-ppc@nongnu.org, david@gibson.dropbear.id.au,
	rth@twiddle.net
Cc: programmingkidx@gmail.com, alex.bennee@linaro.org,
	qemu-devel@nongnu.org, bharata@linux.vnet.ibm.com
Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH RFC v1 0/3] Enable MTTCG on PPC64
Date: Mon, 10 Apr 2017 18:59:21 +0200	[thread overview]
Message-ID: <82645aee-06a5-6187-5548-6b2e0caec5d9@kaod.org> (raw)
In-Reply-To: <87d1ck2ovp.fsf@abhimanyu.i-did-not-set--mail-host-address--so-tickle-me>

On 04/10/2017 06:44 PM, Nikunj A Dadhania wrote:
> Cédric Le Goater <clg@kaod.org> 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 <clg@kaod.org> 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.
> 
> I have got your powernv-ipmi-2.9 + ppc64 mttcg patches, and testing
> them. I too saw delay during boot, but wasn't aware that its caused by
> mttcg. I will have a look.

You can use David's branch directly now, there is enough support.

I am not sure where that is exactly, the kernel is somewhere in
early_setup(). It might be the secondary spinloop.

thanks, 

C. 