From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from AM1EHSOBE002.bigfish.com (am1ehsobe002.messaging.microsoft.com [213.199.154.205]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "mail.global.frontbridge.com", Issuer "Microsoft Secure Server Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id 3F588B6FAB for ; Tue, 24 Jan 2012 06:31:44 +1100 (EST) Message-ID: <4F1DB597.7030506@freescale.com> Date: Mon, 23 Jan 2012 13:31:35 -0600 From: Scott Wood MIME-Version: 1.0 To: Benjamin Herrenschmidt Subject: Re: [PATCH] powerpc/booke64: Configurable lazy interrupt disabling References: <1326897306-3924-1-git-send-email-Laurentiu.Tudor@freescale.com> <1326921026.26116.34.camel@pasglop> <1327100531.2923.3.camel@pasglop> In-Reply-To: <1327100531.2923.3.camel@pasglop> Content-Type: text/plain; charset="ISO-8859-1" Cc: Laurentiu Tudor , linuxppc-dev@lists.ozlabs.org, Stuart Yoder List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 01/20/2012 05:02 PM, Benjamin Herrenschmidt wrote: > >> With Topaz, interrupts go directly to guests and we don't want to require a >> trap/hcall to do an IACK, as that adds potentially thousands of cycles of >> latency to every interrupt. >> >> As you know, with external proxy interrupts are acknowledged by the >> hardware and it becomes problematic to replay the interrupt in >> the context of lazy EE when interrupts are re-enabled. The interrupt >> will not fire again when you enable EE. > > So you have a broken HW and broken HV design to start with ... :-) That "breakage" significantly reduces the overhead of handling interrupts in a guest, since we don't need to involve the hypervisor (at least on the entry side -- there's a hack to avoid it on EOI as well, though that involves exposing some MPIC registers directly; users can decide whether it's worth enabling for their use case). -Scott