From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52772) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XLvxI-0008DE-Ad for qemu-devel@nongnu.org; Mon, 25 Aug 2014 11:13:20 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XLvxA-0004tM-3n for qemu-devel@nongnu.org; Mon, 25 Aug 2014 11:13:12 -0400 Received: from mail1.windriver.com ([147.11.146.13]:48785) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XLvx9-0004t5-Sm for qemu-devel@nongnu.org; Mon, 25 Aug 2014 11:13:04 -0400 Message-ID: <53FB5276.7050003@windriver.com> Date: Mon, 25 Aug 2014 09:12:54 -0600 From: Chris Friesen MIME-Version: 1.0 References: <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> <20140721161034.GC22161@irqsave.net> <53F7E77A.9050509@windriver.com> <20140823075658.GA6687@irqsave.net> In-Reply-To: <20140823075658.GA6687@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 08/23/2014 01:56 AM, Beno=EEt Canet wrote: > The Friday 22 Aug 2014 =E0 18:59:38 (-0600), Chris Friesen wrote : >> On 07/21/2014 10:10 AM, 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 throt= tling 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 memor= y, 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-ca= se would >>> >>> Sorry I didn't understood this part at first read. >>> >>> In the linux guest can you monitor: >>> benoit@Laure:~$ cat /sys/class/block/xyz/inflight ? >>> >>> This would give us a faily precise number of the requests actually in= flight between the guest and qemu. >> >> >> After a bit of a break I'm looking at this again. >> > > Strange. > > I would use dd with the flag oflag=3Dnocache to make sure the write req= uest > does not do in the guest cache though. I set up another test, checking the inflight value every second. Running just "dd if=3D/dev/zero of=3Dtestfile2 bs=3D1M count=3D700=20 oflag=3Dnocache&" gave a bit over 100 inflight requests. If I simultaneously run "dd if=3Dtestfile of=3D/dev/null bs=3D1M count=3D= 700=20 oflag=3Dnocache&" then then number of inflight write requests peaks at 17= 6. I should point out that the above numbers are with qemu 1.7.0, with a=20 ceph storage backend. qemu is started with -drive file=3Drbd:cinder-volumes/......... Chris