From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58700) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YH96V-000760-OL for qemu-devel@nongnu.org; Fri, 30 Jan 2015 05:47:12 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YH96Q-0001Ym-OJ for qemu-devel@nongnu.org; Fri, 30 Jan 2015 05:47:11 -0500 Received: from goliath.siemens.de ([192.35.17.28]:53618) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YH96Q-0001Yb-Cq for qemu-devel@nongnu.org; Fri, 30 Jan 2015 05:47:06 -0500 Message-ID: <54CB6126.5080700@siemens.com> Date: Fri, 30 Jan 2015 11:47:02 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <20150129203728.6cb9271e@crunchbang> <54CABD0A.1090207@redhat.com> <54CB34CB.20805@siemens.com> <20150130112644.3ab44d84@crunchbang> <54CB5EB5.7050902@greensocs.com> In-Reply-To: <54CB5EB5.7050902@greensocs.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] QEMU and Real Time OS List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Frederic Konrad , =?UTF-8?B?TWFyYyBNYXLDrQ==?= Cc: Paolo Bonzini , Marcelo Tosatti , qemu-devel , Luiz Capitulino On 2015-01-30 11:36, Frederic Konrad wrote: > On 30/01/2015 11:26, Marc Mar=C3=AD wrote: >> El Fri, 30 Jan 2015 08:37:47 +0100 >> Jan Kiszka escribi=C3=B3: >>> On 2015-01-30 00:06, Paolo Bonzini wrote: >>>> >>>> On 29/01/2015 20:37, Marc Mar=C3=AD wrote: >>>>> Is this an expected behaviour? I can't see why. >>>>> >>>>> I'd like to know if there is a certain reason why it doesn't work. >>>>> Or if it should work and the problem is too much I/O overhead. Or >>>>> any other hint to understand it. >>>> It is due to latencies in the host. You need at least to use >>>> preempt-rt kernels in the host as well. >>> That alone won't help much. You also need to fine-tune the guest to >>> avoid running into QEMU locks that continuously synchronizes the gues= t >>> on things like VGA or disk I/O emulation. >>> >>> When using KVM, thus being able to run VCPUs widely independent of >>> each other and the device models, you need to push cyclictest on an >>> isolated second virtual CPU of the guest. Luiz and Marcelo can >>> probably confirm this based on their ongoing experiments. >>> >>> With TCG, we would first of all have to make it true SMP and >>> independent of the I/O device lock. That's what Frederic is working >>> on [1]. >>> >>> Jan >>> >>> [1] http://permalink.gmane.org/gmane.comp.emulators.qemu/314406 >>> >> Thanks for the answers. I think I'm stuck with ARM926, which I think i= s >> not prepared for SMP. I'll have to look if I can use Cortex for my >> experiments. >> >> I'll continue interested with the improvements for RT on TCG, but for >> the moment I'll go to work on real harware, even though is easier to >> run and debug on an emulator. >> >> Thanks >> Marc > Hi Marc, >=20 > I think the important point here is "TCG thread independent of the I/O > device lock". > I need it for multithread TCG but that doesn't mean you need an SMP gue= st > platform for that. Provided the guest is not stressing any costly device emulation. That can cause priority inversions when an urgent event should rather be delivered in the meantime. That can easily happen when running real-time Linux as guest, therefore the SMP proposal. Jan --=20 Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux