From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx4-phx2.redhat.com (mx4-phx2.redhat.com [209.132.183.25]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3slj3w2Z4MzDskR for ; Fri, 30 Sep 2016 16:59:40 +1000 (AEST) Date: Fri, 30 Sep 2016 02:58:58 -0400 (EDT) From: Paolo Bonzini To: Pan Xinhui Cc: Peter Zijlstra , Christian Borntraeger , Pan Xinhui , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, virtualization@lists.linux-foundation.org, linux-s390@vger.kernel.org, xen-devel-request@lists.xenproject.org, kvm@vger.kernel.org, benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au, mingo@redhat.com, paulmck@linux.vnet.ibm.com, will deacon , kernellwp@gmail.com, jgross@suse.com, bsingharora@gmail.com, Heiko Carstens Message-ID: <2136938368.606190.1475218738567.JavaMail.zimbra@redhat.com> In-Reply-To: <496ba299-1f1d-e98b-7827-f861eeea5558@linux.vnet.ibm.com> References: <1469101514-49475-1-git-send-email-xinhui.pan@linux.vnet.ibm.com> <20160929101040.GV5016@twins.programming.kicks-ass.net> <166f3bad-f700-4624-6c1c-996f90ad609c@de.ibm.com> <20160929103133.GW5016@twins.programming.kicks-ass.net> <496ba299-1f1d-e98b-7827-f861eeea5558@linux.vnet.ibm.com> Subject: Re: [PATCH v3 0/4] implement vcpu preempted check MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , > > > > Please consider s390 and (x86/arm) KVM. Once we have a few, more can > > > > follow later, but I think its important to not only have PPC support for > > > > this. > > > > > > Actually the s390 preemted check via sigp sense running is available for > > > all hypervisors (z/VM, LPAR and KVM) which implies everywhere as you can > > > no longer buy s390 systems without LPAR. > > > > > > As Heiko already pointed out we could simply use a small inline function > > > that calls cpu_is_preempted from arch/s390/lib/spinlock (or > > > smp_vcpu_scheduled from smp.c) > > > > Sure, and I had vague memories of Heiko's email. This patch set however > > completely fails to do that trivial hooking up. > > sorry for that. > I will try to work it out on x86. x86 has no hypervisor support, and I'd like to understand the desired semantics first, so I don't think it should block this series. In particular, there are at least the following choices: 1) exit to userspace (5-10.000 clock cycles best case) counts as lock holder preemption 2) any time the vCPU thread not running counts as lock holder preemption To implement the latter you'd need a hypercall or MSR (at least as a slow path), because the KVM preempt notifier is only active during the KVM_RUN ioctl. Paolo