From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38279) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1X9JZ3-00072x-5p for qemu-devel@nongnu.org; Mon, 21 Jul 2014 15:48:08 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1X9JYv-0003Dd-MT for qemu-devel@nongnu.org; Mon, 21 Jul 2014 15:48:01 -0400 Received: from lputeaux-656-01-25-125.w80-12.abo.wanadoo.fr ([80.12.84.125]:38347 helo=paradis.irqsave.net) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1X9JYv-0003DL-GG for qemu-devel@nongnu.org; Mon, 21 Jul 2014 15:47:53 -0400 Date: Mon, 21 Jul 2014 21:47:11 +0200 From: =?iso-8859-1?Q?Beno=EEt?= Canet Message-ID: <20140721194711.GA22745@irqsave.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <53CD3341.60705@windriver.com> 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: Chris Friesen Cc: =?iso-8859-1?Q?Beno=EEt?= Canet , Paolo Bonzini , qemu-devel@nongnu.org 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 throttli= ng 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 up= 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 show= 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. Best regards Beno=EEt > > > >I think Linux as a limit of 512Kb for io size or something like that. > >So the guest would have VIRTIO_PCI_QUEUE_MAX * 512Kb of in flight buff= ers at max. >=20 > Those numbers don't line up with what we were seeing...we saw a 120MB+ = jump > when running dbench, which would map to more like 2MB per operation ass= uming > a limit of VIRTIO_PCI_QUEUE_MAX (i.e. 64). >=20 > Unless there are other buffers involved that we haven't factored in... >=20 > Chris >=20 >=20