From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:54101) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eo6xi-0007qr-OO for qemu-devel@nongnu.org; Tue, 20 Feb 2018 07:23:59 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eo6xe-0000Ng-QQ for qemu-devel@nongnu.org; Tue, 20 Feb 2018 07:23:58 -0500 Date: Tue, 20 Feb 2018 13:23:29 +0100 From: Cornelia Huck Message-ID: <20180220132329.39d8b759.cohuck@redhat.com> In-Reply-To: <1518797321-28356-1-git-send-email-mihajlov@linux.vnet.ibm.com> References: <1518797321-28356-1-git-send-email-mihajlov@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCHv5 0/5] add query-cpu-fast and related s390 changes List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Viktor Mihajlovski Cc: qemu-devel@nongnu.org, agraf@suse.de, ehabkost@redhat.com, armbru@redhat.com, david@redhat.com, dgilbert@redhat.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, pbonzini@redhat.com, rth@twiddle.net, eblake@redhat.com On Fri, 16 Feb 2018 17:08:36 +0100 Viktor Mihajlovski wrote: > v5 synopsis: Split out HMP changes from Patch 2 into Patch 5. Please > re-review, as I've removed the a-b/r-b from Patch 2 > as well. > > This series consolidates patches around a performance issue > caused by the usage of QMP query-cpus. > > A performance issue was found in an OpenStack environment, where > ceilometer was collecting domain statistics with libvirt. The domain > statistics reported by libvirt include the vCPU halted state, which > in turn is retrieved with QMP query-cpus. > > This causes two issues: > 1. Performance: on most architectures query-cpus needs to issue a KVM ioctl > to find out whether a vCPU was halted. This is not the case for s390 > but query-cpus is always causing the vCPU to exit the VM. > > 2. Semantics: on x86 and other architectures, halted is a highly transient > state, which is likely to have already changed shortly after the state > information has been retrieved. This is not the case for s390, where > halted is an indication that the vCPU is stopped, meaning its not > available to the guest operating system until it has been restarted. Thanks, queued to s390-next.