From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id DB80C2C007E for ; Wed, 11 Jul 2012 10:53:23 +1000 (EST) Message-ID: <1341967996.18850.20.camel@pasglop> Subject: Re: [PATCH] powerpc/booke: Eliminate rfi from exception entry path. From: Benjamin Herrenschmidt To: Scott Wood Date: Wed, 11 Jul 2012 10:53:16 +1000 In-Reply-To: <4FFCCBAD.40504@freescale.com> References: <20120711003454.GA22757@tyr.buserror.net> <1341967010.18850.19.camel@pasglop> <4FFCCBAD.40504@freescale.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: linuxppc-dev@lists.ozlabs.org, Alexander Graf , Stuart Yoder List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 2012-07-10 at 19:41 -0500, Scott Wood wrote: > On 07/10/2012 07:36 PM, Benjamin Herrenschmidt wrote: > > On Tue, 2012-07-10 at 19:34 -0500, Scott Wood wrote: > >> Unlike classic, we don't really need the MSR change to be atomic with the > >> branch. This eliminates a trap as a KVM guest (in the absence of > >> hardware hypervisor extensions), where mtmsr is paravirtualized but rfi > >> is not. For a virtualized guest without any paravirtualization, this > >> eliminates an additional two traps (SRR0/1). > > > > In fact, I wonder, what do we write into the MSR at this point that > > wasn't already in it in BookE ? RI ? I wonder if we could get away > > without the mtmsr alltogether... > > Doesn't EE get set there for some exceptions? It does, tho arguably it shouldn't in most cases :-) I'm happy to turn a bunch of these into explicit local_irq_enable() in the C code though which will turn into a wrteei which is more efficient on BookE. Cheers, Ben.