From mboxrd@z Thu Jan 1 00:00:00 1970 From: Purcareata Bogdan Subject: Re: [PATCH 0/2] powerpc/kvm: Enable running guests on RT Linux Date: Mon, 23 Feb 2015 10:12:42 +0200 Message-ID: <54EAE0FA.3090402@freescale.com> 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> <54E74E77.2070503@redhat.com> <54E74FED.2090203@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Cc: , , , Thomas Gleixner To: Sebastian Andrzej Siewior , Paolo Bonzini , Alexander Graf , Bogdan Purcareata , , Return-path: In-Reply-To: <54E74FED.2090203@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-rt-users.vger.kernel.org On 20.02.2015 17:17, Sebastian Andrzej Siewior wrote: > On 02/20/2015 04:10 PM, Paolo Bonzini wrote: >> 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 Actually, it's not just netperf. The bug triggers in the following scenarios: - running CPU intensive task (while true; do date; done) in SMP guest (even with 2 VCPUs) - running netperf in guest - running cyclictest in SMP guest > May I please see a backtrace with context tracking which states where > the interrupts / preemption gets disabled and where the lock was taken? Will do, I will get back to you as soon as I have it available. I will try and capture it using function trace. > I'm not totally against this patch I just want to make sure this is not > a blind raw conversation to shup up the warning the kernel throws. > >> 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. > good :) > >> >> Paolo >> > Sebastian >