From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-x230.google.com (mail-wi0-x230.google.com [IPv6:2a00:1450:400c:c05::230]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id E17C61A13D7 for ; Sat, 21 Feb 2015 02:10:54 +1100 (AEDT) Received: by mail-wi0-f176.google.com with SMTP id h11so3591267wiw.3 for ; Fri, 20 Feb 2015 07:10:51 -0800 (PST) Sender: Paolo Bonzini Message-ID: <54E74E77.2070503@redhat.com> Date: Fri, 20 Feb 2015 16:10:47 +0100 From: Paolo Bonzini MIME-Version: 1.0 To: Sebastian Andrzej Siewior , Alexander Graf , Bogdan Purcareata , linuxppc-dev@lists.ozlabs.org, linux-rt-users@vger.kernel.org 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 Cc: scottwood@freescale.com, mihai.caraman@freescale.com, Thomas Gleixner , linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 >