From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 55F041A007D for ; Fri, 23 May 2014 20:00:25 +1000 (EST) Message-ID: <1400839224.28224.5.camel@ale.ozlabs.ibm.com> Subject: Re: [PATCH v2 0/6] Implement split core for POWER8 From: Michael Neuling To: Alexander Graf Date: Fri, 23 May 2014 20:00:24 +1000 In-Reply-To: <537F1A8D.9000704@suse.de> References: <1400832930-17050-1-git-send-email-mikey@neuling.org> <537F1A8D.9000704@suse.de> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, Paul Mackerras , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 2014-05-23 at 11:53 +0200, Alexander Graf wrote: > On 23.05.14 10:15, Michael Neuling wrote: > > This patch series implements split core mode on POWER8. This enables u= p to 4 > > subcores per core which can each independently run guests (per guest SP= Rs like > > SDR1, LPIDR etc are replicated per subcore). Lots more documentation o= n this > > feature in the code and commit messages. > > > > Most of this code is in the powernv platform but there's a couple of KV= M > > specific patches too. > > > > Patch series authored by mpe and me with a few bug fixes from others. > > > > v2: > > There are some minor updates based on comments and I've added the Ac= ks by > > Paulus and Alex for the KVM code. >=20 > I don't see changelogs inside the individual patches. Please make sure= =20 > to always mention what changed from one version to the next in a=20 > particular patch, so that I have the chance to check whether that change= =20 > was good :). Sure, that was a bit sloppy Only the last patch was the only one that changed. I changed the sysfs file from 600 permissions to 644 so that users can read it more easily as requested by Joel. The other change was to fix the possibility of a race when coming out of nap and checking if we need to split. This fix was form paulus' (worked offline). > Also, is there any performance penalty associated with split core mode?= =20 > If not, could we just always default to split-by-4 on POWER8 bare metal? Yeah, there is a performance hit . When you are split (ie subcores_per_core =3D 2 or 4), the core is stuck in SMT8 mode. So if you only have 1 thread active (others napped), you won't get the benefit of ST mode in the core (more register renames per HW thread, more FXUs, more FPUs etc). Mikey