Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754824AbbBTO5x (ORCPT ); Fri, 20 Feb 2015 09:57:53 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48437 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753762AbbBTO5w (ORCPT ); Fri, 20 Feb 2015 09:57:52 -0500 Message-ID: <54E74B58.90706@redhat.com> Date: Fri, 20 Feb 2015 15:57:28 +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> In-Reply-To: <54E74A8C.30802@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: 1217 Lines: 28 On 20/02/2015 15:54, Sebastian Andrzej Siewior wrote: > Usually you see "scheduling while atomic" on -RT and convert them to > raw locks if it is appropriate. > > Bogdan wrote in 2/2 that he needs to limit the number of CPUs in oder > not cause a DoS and large latencies in the host. I haven't seen an > answer to my why question. Because if the conversation leads to > large latencies in the host then it does not look right. > > Each host PIC has a rawlock and does mostly just mask/unmask and the > raw lock makes sure the value written is not mixed up due to > preemption. > This hardly increase latencies because the "locked" path is very short. > If this conversation leads to higher latencies then the locked path is > too long and hardly suitable to become a rawlock. 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. Paolo -- 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/