From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:36028) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TELY4-0001jO-IZ for qemu-devel@nongnu.org; Wed, 19 Sep 2012 10:46:45 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TELXy-0005pU-M0 for qemu-devel@nongnu.org; Wed, 19 Sep 2012 10:46:44 -0400 Received: from david.siemens.de ([192.35.17.14]:23164) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TELXy-0005on-Bj for qemu-devel@nongnu.org; Wed, 19 Sep 2012 10:46:38 -0400 Message-ID: <5059DAC4.9020907@siemens.com> Date: Wed, 19 Sep 2012 16:46:28 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <50587258.9090303@siemens.com> <20120919133720.GB22659@snow> <5059D26E.2050808@siemens.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Will the ELI incorporated in theKVM? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Abel Gordon Cc: Nadav Har'El , GaoYi , "qemu-devel@nongnu.org" , Michael D Day , Avi Kivity , Muli Ben-Yehuda , Nadav Amit On 2012-09-19 16:43, Abel Gordon wrote: > >> It's imperfect as you need to dedicate a core to pure guest-mode load >> and cannot run userspace on that core (cannot walk through >> userspace-based device models e.g.). > > That's not correct. > For the evaluation, we dedicated a core for each guest to maximize the > performance but this > is not a requirement. You can over-commit cores and share them across > multiple VMs. In this case, > you will be sharing the cycles among all the VMs and the performance per VM > will be degraded. > In addition, if you share a core, an interrupt for a guest may be raised > while the corresponding > VCPU is not running. Depending on the workload, most of the interrupts will > be generated while > the VCPU runs or not. > >> and cannot run userspace on that core (cannot walk through >> userspace-based device models e.g.). > > That's not correct. > We can run any thread (including user-space threads) on the same core we > run the VMs (VCPU threads). > In fact, we did that for the ELI evaluation: we shared a single core to run > the VCPU thread and ALL the host threads (including qemu I/O thread). > >> And it requires that magic bar to >> map the shadow IDT into the guest (hmm, I think Hitachi avoided this). > > Hitachi uses a different technique which seems to have the 2 disadvantages > you previously mentioned while ELI doesn't have these disadvantages. > >> It's invasive as it has to change Linux to maintain those isolated slave >> CPUs. That is, of course, based on code that was published by Hitachi. >> Yours may differ but will still have to solve the same problems. > > ELI does not require isolated/slave CPUs. > OK. Show patches. Jan -- Siemens AG, Corporate Technology, CT RTC ITP SDP-DE Corporate Competence Center Embedded Linux