Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754492AbbBTPKy (ORCPT ); Fri, 20 Feb 2015 10:10:54 -0500 Received: from mail-wg0-f48.google.com ([74.125.82.48]:46488 "EHLO mail-wg0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751870AbbBTPKx (ORCPT ); Fri, 20 Feb 2015 10:10:53 -0500 Message-ID: <54E74E77.2070503@redhat.com> Date: Fri, 20 Feb 2015 16:10:47 +0100 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: Sebastian Andrzej Siewior , Alexander Graf , Bogdan Purcareata , linuxppc-dev@lists.ozlabs.org, linux-rt-users@vger.kernel.org CC: linux-kernel@vger.kernel.org, scottwood@freescale.com, mihai.caraman@freescale.com, Thomas Gleixner Subject: Re: [PATCH 0/2] powerpc/kvm: Enable running guests on RT Linux References: <1424251955-308-1-git-send-email-bogdan.purcareata@freescale.com> <54E73A6C.9080500@suse.de> <54E740E7.5090806@redhat.com> <54E74A8C.30802@linutronix.de> <54E74B58.90706@redhat.com> <54E74D5E.1050209@linutronix.de> In-Reply-To: <54E74D5E.1050209@linutronix.de> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1719 Lines: 48 On 20/02/2015 16:06, Sebastian Andrzej Siewior wrote: > On 02/20/2015 03:57 PM, Paolo Bonzini wrote: >> Yes, but large latencies just mean the code has to be rewritten (x86 >> doesn't anymore do event injection in an atomic regions for example). >> Until it is, using raw_spin_lock is correct. > > It does not sound like it. It sounds more like disabling interrupts to > get things run faster and then limit it on a different corner to not > blow up everything. "This patchset enables running KVM SMP guests with external interrupts on an underlying RT-enabled Linux. Previous to this patch, a guest with in-kernel MPIC emulation could easily panic the kernel due to preemption when delivering IPIs and external interrupts, because of the openpic spinlock becoming a sleeping mutex on PREEMPT_RT_FULL Linux". > Max latencies was decreased "Max latency (us) 70 62" and that > is why this is done? For 8 us and possible DoS in case there are too > many cpus? My understanding is that: 1) netperf can get you a BUG KVM, and raw_spinlock fixes that 2) cyclictest did not trigger the BUG, and you can also get reduced latency from using raw_spinlock. I think we agree that (2) is not a factor in accepting the patch. Paolo >> Paolo >> > > Sebastian > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- 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/