From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56184) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1X9Kt7-0003NV-CH for qemu-devel@nongnu.org; Mon, 21 Jul 2014 17:12:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1X9Ksy-0004zK-VX for qemu-devel@nongnu.org; Mon, 21 Jul 2014 17:12:49 -0400 Received: from mail1.windriver.com ([147.11.146.13]:37054) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1X9Ksy-0004zA-NV for qemu-devel@nongnu.org; Mon, 21 Jul 2014 17:12:40 -0400 Message-ID: <53CD823F.7090402@windriver.com> Date: Mon, 21 Jul 2014 15:12:31 -0600 From: Chris Friesen MIME-Version: 1.0 References: <53C949BA.9040204@windriver.com> <53C97FEB.9060208@redhat.com> <53C9A440.7020306@windriver.com> <53CA06ED.1090102@redhat.com> <53CA0FC4.8080802@windriver.com> <53CA1D06.9090601@redhat.com> <20140719084537.GA3058@irqsave.net> <53CD2AE1.6080803@windriver.com> <20140721151540.GA22161@irqsave.net> <53CD3341.60705@windriver.com> <20140721194711.GA22745@irqsave.net> In-Reply-To: <20140721194711.GA22745@irqsave.net> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] is there a limit on the number of in-flight I/O operations? List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?ISO-8859-1?Q?Beno=EEt_Canet?= Cc: Paolo Bonzini , qemu-devel@nongnu.org On 07/21/2014 01:47 PM, Beno=EEt Canet wrote: > The Monday 21 Jul 2014 =E0 09:35:29 (-0600), Chris Friesen wrote : >> On 07/21/2014 09:15 AM, Beno=EEt Canet wrote: >>> The Monday 21 Jul 2014 =E0 08:59:45 (-0600), Chris Friesen wrote : >>>> On 07/19/2014 02:45 AM, Beno=EEt Canet wrote: >>>> >>>>> I think in the throttling case the number of in flight operation is= limited by >>>>> the emulated hardware queue. Else request would pile up and throttl= ing would be >>>>> inefective. >>>>> >>>>> So this number should be around: #define VIRTIO_PCI_QUEUE_MAX 64 or= something like than that. >>>> >>>> Okay, that makes sense. Do you know how much data can be written as= part of >>>> a single operation? We're using 2MB hugepages for the guest memory,= and we >>>> saw the qemu RSS numbers jump from 25-30MB during normal operation u= p to >>>> 120-180MB when running dbench. I'd like to know what the worst-case= would >>>> be. > > At first start QEMU start only a bunch of IO threads. > When IOs activity kick some other IO threads will be started and can sh= ow up in > memory measurement because the same physical memory will be referenced = by multiple threads. > > Are you sure this is not the case you are seeing ? > > The H option of ps on the host could help. I'm pretty sure that this wouldn't change the RES (aka RSS) value, since=20 all those threads are sharing the same address space. If we create IO threads on activity though, we could end up causing some=20 overhead due to the per-thread stack (8MB by default). Do we have a=20 limit on how many IO threads could get created? Chris