Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753303AbbHZPlw (ORCPT ); Wed, 26 Aug 2015 11:41:52 -0400 Received: from mailapp01.imgtec.com ([195.59.15.196]:30073 "EHLO mailapp01.imgtec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751697AbbHZPlv (ORCPT ); Wed, 26 Aug 2015 11:41:51 -0400 Subject: Re: [PATCH 01/10] irqchip: irq-mips-gic: export gic_send_ipi To: Thomas Gleixner References: <1440419959-14315-1-git-send-email-qais.yousef@imgtec.com> <1440419959-14315-2-git-send-email-qais.yousef@imgtec.com> <55DB15EB.3090109@imgtec.com> <55DB1CD2.5030300@arm.com> <55DB29B5.3010202@imgtec.com> <55DB48C9.7010508@imgtec.com> <55DB519D.2090203@arm.com> <55DDA1C4.4070301@imgtec.com> <55DDD3E3.7070009@imgtec.com> CC: Marc Zyngier , "alsa-devel@alsa-project.org" , Jason Cooper , "linux-kernel@vger.kernel.org" , "linux-mips@linux-mips.org" , Mark Rutland From: Qais Yousef Message-ID: <55DDDE3C.8030609@imgtec.com> Date: Wed, 26 Aug 2015 16:41:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.154.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3091 Lines: 73 On 08/26/2015 04:08 PM, Thomas Gleixner wrote: > On Wed, 26 Aug 2015, Qais Yousef wrote: >> On 08/26/2015 02:19 PM, Thomas Gleixner wrote: >>> Wrong. You cannot move an IPI around with set_affinity. It's possible >>> to send an IPI to more than one target CPU, but that has nothing to do >>> with affinities. >>> >>> Are you talking about IPIs or about general interrupts which have an >>> affinity setting? >> Maybe my view of the world is limited. I wrote this because the mechanism to >> route an IPI and set affinities is the same. > That might be the case on your particular platform, but that's not > generally true. > >> So specifying which core or hardware thread should Linux CPU route this IPI to >> is the same as setting the affinity, no? Linux will not move the IPI that is >> routed to the coprocessor core. Just the IPI it will receive. >> >> Also the way I see it is that this is an external interrupt whether it was >> asserted by real signal or through IPI mechanism and it should be treated as >> such in terms of moving inside Linux SMP, no? Again maybe my view of the world >> is limited but I can't see why migrating the interrupt would affect >> correctness unless there's a hardware limitation like only core 0 can read >> info from AXD (which is where my suggestion to using affinity hint above to >> accommodate such limitations). >> >> When you say 'It is possible to send an IPI to more than one target CPU', is >> it a case we need to cater for? The way I was seeing this problem is >> communication between single Linux SMP and a single coprocessor unit. I didn't >> think of it as single to many. Even if the coprocessor is a cluster I'd expect >> it to act as a single unit like Linux SMP. And if it wanted to send 2 >> different interrupts it will need to use 2 different IPIs. > You are confusing the terms. > > IPI = Inter Processor Interrupt > > As the name says that's an interrupt which goes from one cpu to > another. So an IPI has a very clear target. OK understood. My interpretation of the processor here was the difference. I was viewing the whole linux cpus as one unit with regard to its coprocessors. > > Whether the platform implements IPIs via general interrupts which are > made affine to a particular cpu or some other specialized mechanism is > completely irrelevant. An IPI is not subject to affinity settings, > period. > > So if you want to use an IPI then you need a target cpu for that IPI. > > If you want something which can be affined to any cpu, then you need a > general interrupt and not an IPI. We are using IPIs to exchange interrupts. Affinity is not important to me. Thanks, Qais > > That's what I asked before and you still did not answer that question. > >>> Are you talking about IPIs or about general interrupts which have an >>> affinity setting? > Thanks, > > tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/