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

From: Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>
To: "Cédric Le Goater" <clg@kaod.org>,
	qemu-ppc@nongnu.org, alex.bennee@linaro.org,
	david@gibson.dropbear.id.au, rth@twiddle.net
Cc: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH RFC 0/4] Enable MTTCG on PowerPC
Date: Fri, 02 Sep 2016 12:16:59 +0530	[thread overview]
Message-ID: <871t12lrx8.fsf@abhimanyu.i-did-not-set--mail-host-address--so-tickle-me> (raw)
In-Reply-To: <a6466aec-032a-7404-08f5-5260741246de@kaod.org>

Cédric Le Goater <clg@kaod.org> writes:

> 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 :

I see this as a temporary workaround, need to fix it.

> 	{	/* Power8 DD1: Does not support doorbell IPIs */
> 		.pvr_mask		= 0xffffff00,
> 		.pvr_value		= 0x004d0100,
> 		.cpu_name		= "POWER8 (raw)",
> 		.cpu_features		= CPU_FTRS_POWER8_DD1,
> 		...

Regards
Nikunj