From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paolo Bonzini Subject: Re: [PATCH 0/2] powerpc/kvm: Enable running guests on RT Linux Date: Thu, 26 Feb 2015 14:02:38 +0100 Message-ID: <54EF196E.4090805@redhat.com> References: <1424251955-308-1-git-send-email-bogdan.purcareata@freescale.com> <54E73A6C.9080500@suse.de> <54E740E7.5090806@redhat.com> <54E74A8C.30802@linutronix.de> <1424734051.4698.17.camel@freescale.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Cc: Alexander Graf , Bogdan Purcareata , linuxppc-dev@lists.ozlabs.org, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, mihai.caraman@freescale.com, Thomas Gleixner To: Scott Wood , Sebastian Andrzej Siewior Return-path: In-Reply-To: <1424734051.4698.17.camel@freescale.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org On 24/02/2015 00:27, Scott Wood wrote: > This isn't a host PIC driver. It's guest PIC emulation, some of which > is indeed not suitable for a rawlock (in particular, openpic_update_irq > which loops on the number of vcpus, with a loop body that calls > IRQ_check() which loops over all pending IRQs). The question is what behavior is wanted of code that isn't quite RT-ready. What is preferred, bugs or bad latency? If the answer is bad latency (which can be avoided simply by not running KVM on a RT kernel in production), patch 1 can be applied. If the answer is bugs, patch 1 is not upstream material. I myself prefer to have bad latency; if something takes a spinlock in atomic context, that spinlock should be raw. If it hurts (latency), don't do it (use the affected code). Paolo > The vcpu limits are a > temporary bandaid to avoid the worst latencies, but I'm still skeptical > about this being upstream material.