From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Date: Thu, 09 May 2013 22:01:38 +0000 Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts Message-Id: <1368136898.3715.12.camel@pasglop> List-Id: References: <51885F49.6060605@windriver.com> (from tiejun.chen@windriver.com on Mon May 6 20:56:25 2013) <1367892390.3398.12@snotra> <300B73AA675FCE4A93EB4FC1D42459FF3F00D0@039-SN2MPN1-013.039d.mgd.msft.net> <6A3DF150A5B70D4F9B66A25E3F7C888D0700E64A@039-SN2MPN1-011.039d.mgd.msft.net> <518B7014.1090508@windriver.com> <1368103062.25488.193.camel@pasglop> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: David Laight Cc: "tiejun.chen" , Caraman Mihai Claudiu-B02008 , kvm@vger.kernel.org, Wood Scott-B07421 , agraf@suse.de, kvm-ppc@vger.kernel.org, Bhushan Bharat-R65777 , linuxppc-dev@lists.ozlabs.org On Thu, 2013-05-09 at 14:28 +0100, David Laight wrote: > That will happen if the IRQ goes away while the cpu is performing > the IACK sequence. > If the IRQ goes away while the cpu has interrupts masked then > the cpu won't start the interrupt sequence and then try to > read a vector when no interrupt is pending. Right, and get a spurrious vector which shouldn't be a big deal. We tend to call that a "short interrupt". There have been many other cases of short interrupts in the past, for example on some MPICs, when distribution is enabled, they occasionally shoot an interrupt to more than one CPU at once :-) Cheers, Ben. 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 9DC8D2C00F4 for ; Fri, 10 May 2013 08:01:53 +1000 (EST) Message-ID: <1368136898.3715.12.camel@pasglop> Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts From: Benjamin Herrenschmidt To: David Laight Date: Fri, 10 May 2013 08:01:38 +1000 In-Reply-To: References: <51885F49.6060605@windriver.com> (from tiejun.chen@windriver.com on Mon May 6 20:56:25 2013) <1367892390.3398.12@snotra> <300B73AA675FCE4A93EB4FC1D42459FF3F00D0@039-SN2MPN1-013.039d.mgd.msft.net> <6A3DF150A5B70D4F9B66A25E3F7C888D0700E64A@039-SN2MPN1-011.039d.mgd.msft.net> <518B7014.1090508@windriver.com> <1368103062.25488.193.camel@pasglop> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: Wood Scott-B07421 , kvm@vger.kernel.org, Caraman Mihai Claudiu-B02008 , agraf@suse.de, kvm-ppc@vger.kernel.org, "tiejun.chen" , Bhushan Bharat-R65777 , linuxppc-dev@lists.ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Thu, 2013-05-09 at 14:28 +0100, David Laight wrote: > That will happen if the IRQ goes away while the cpu is performing > the IACK sequence. > If the IRQ goes away while the cpu has interrupts masked then > the cpu won't start the interrupt sequence and then try to > read a vector when no interrupt is pending. Right, and get a spurrious vector which shouldn't be a big deal. We tend to call that a "short interrupt". There have been many other cases of short interrupts in the past, for example on some MPICs, when distribution is enabled, they occasionally shoot an interrupt to more than one CPU at once :-) Cheers, Ben. From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts Date: Fri, 10 May 2013 08:01:38 +1000 Message-ID: <1368136898.3715.12.camel@pasglop> References: <51885F49.6060605@windriver.com> (from tiejun.chen@windriver.com on Mon May 6 20:56:25 2013) <1367892390.3398.12@snotra> <300B73AA675FCE4A93EB4FC1D42459FF3F00D0@039-SN2MPN1-013.039d.mgd.msft.net> <6A3DF150A5B70D4F9B66A25E3F7C888D0700E64A@039-SN2MPN1-011.039d.mgd.msft.net> <518B7014.1090508@windriver.com> <1368103062.25488.193.camel@pasglop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: "tiejun.chen" , Caraman Mihai Claudiu-B02008 , kvm@vger.kernel.org, Wood Scott-B07421 , agraf@suse.de, kvm-ppc@vger.kernel.org, Bhushan Bharat-R65777 , linuxppc-dev@lists.ozlabs.org To: David Laight Return-path: In-Reply-To: Sender: kvm-ppc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, 2013-05-09 at 14:28 +0100, David Laight wrote: > That will happen if the IRQ goes away while the cpu is performing > the IACK sequence. > If the IRQ goes away while the cpu has interrupts masked then > the cpu won't start the interrupt sequence and then try to > read a vector when no interrupt is pending. Right, and get a spurrious vector which shouldn't be a big deal. We tend to call that a "short interrupt". There have been many other cases of short interrupts in the past, for example on some MPICs, when distribution is enabled, they occasionally shoot an interrupt to more than one CPU at once :-) Cheers, Ben.