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Re: [PATCH v4] target/ppc: Add POWER9 DD2.2 model

From: Nicholas Piggin
Subject: Re: [PATCH v4] target/ppc: Add POWER9 DD2.2 model
Date: Tue, 16 May 2023 19:57:34 +1000

On Tue May 16, 2023 at 6:44 PM AEST, Cédric Le Goater wrote:
> On 5/15/23 18:02, Nicholas Piggin wrote:
> > POWER9 DD2.1 and earlier had significant limitations when running KVM,
> > including lack of "mixed mode" MMU support (ability to run HPT and RPT
> > mode on threads of the same core), and a translation prefetch issue
> > which is worked around by disabling "AIL" mode for the guest.
> > 
> > These processors are not widely available, and it's difficult to deal
> > with all these quirks in qemu +/- KVM, so create a POWER9 DD2.2 CPU
> > and make it the default POWER9 CPU.
> I would remove power9_v1.0 and power9_v2.0 (not shipped AFAIK) and maybe
> add power9_v2.3 since it has a little more features.

Yes to removing DD1 (and for P10), and adding 2.3. Not sure about
removing 2.0, we carry this radix MMU prefetch workaround thing for
2.0 and 2.1 in upstream KVM which causes some of this AIL-3

Having a 2.0 model might help with that, and if it doesn't cause
much effort to maintain I'd like to keep it for a bit. Can remove
it if upstream KVM drops support or it causes problems.


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