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 A8F7E2C007E for ; Wed, 11 Jul 2012 10:54:24 +1000 (EST) Message-ID: <1341968057.18850.21.camel@pasglop> Subject: Re: [PATCH] powerpc/booke: Eliminate rfi from exception entry path. From: Benjamin Herrenschmidt To: Scott Wood Date: Wed, 11 Jul 2012 10:54:17 +1000 In-Reply-To: <4FFCCD2D.20407@freescale.com> References: <20120711003454.GA22757@tyr.buserror.net> <4FFCCD2D.20407@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 19:47 -0500, Scott Wood wrote: > On 07/10/2012 07:44 PM, Alexander Graf wrote: > > > > On 11.07.2012, at 02:34, Scott Wood wrote: > >> +#ifdef CONFIG_BOOKE > >> + /* > >> + * We're not changing address space on Book E, and the extra rfi > >> + * can hurt when virtualized without hardware support -- whereas > >> + * mtmsr can be paravirtualized. > > > > We can always paravirtualize RFI as well if it makes sense. > > I'm not sure that's possible. We thought about it a while back, but > IIRC the difficulty was not leaving a register clobbered. Besides mtmsr is slow on real HW as well. Also paravirt as done today for complex instructions like mtmsr is racy :-) (I already had a chat about that with Alex a while back, we might want to re-consider what kind of fix can be done at some point). Cheers, Ben.