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bh=tPThpVxbz3Hrt8hS7fDRgcAziVHgUNLKIZBRXF8Zd6Y=; b=F/Rild7JN+jPWlgd0mxZouxVEM0ideBq09lJ5M5/uPLlDuryA/p3Zk37CUMntt72O73x5D F2VCy+KjvOqB3yPqafwpuZ/vNgLRwCknTtc6W/VMoRTQaYqB0kJoDRYSnywibiXy2d/k3P 6LFa5w0nJ4kO9bCiE3n9enorJyLIEsc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-106-04vaEqjiNqmj0g9Ia7285A-1; Wed, 23 Sep 2020 11:55:27 -0400 X-MC-Unique: 04vaEqjiNqmj0g9Ia7285A-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EDA2F1007474; Wed, 23 Sep 2020 15:55:25 +0000 (UTC) Received: from linux.fritz.box (ovpn-112-239.ams2.redhat.com [10.36.112.239]) by smtp.corp.redhat.com (Postfix) with ESMTPS id BC5C873668; Wed, 23 Sep 2020 15:55:24 +0000 (UTC) Date: Wed, 23 Sep 2020 17:55:22 +0200 From: Kevin Wolf To: Alberto Garcia Subject: Re: [PATCH] docs: Document the throttle block filter Message-ID: <20200923155522.GF6912@linux.fritz.box> References: <20200921173016.27935-1-berto@igalia.com> MIME-Version: 1.0 In-Reply-To: <20200921173016.27935-1-berto@igalia.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/23 00:53:58 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -32 X-Spam_score: -3.3 X-Spam_bar: --- X-Spam_report: (-3.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.228, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 21.09.2020 um 19:30 hat Alberto Garcia geschrieben: > This filter was added back in 2017 for QEMU 2.11 but it was never > properly documented, so let's explain how it works and add a couple of > examples. > > Signed-off-by: Alberto Garcia > --- > docs/throttle.txt | 107 +++++++++++++++++++++++++++++++++++++++++++++- > 1 file changed, 106 insertions(+), 1 deletion(-) > > diff --git a/docs/throttle.txt b/docs/throttle.txt > index cd4e109d39..c06d1b9662 100644 > --- a/docs/throttle.txt > +++ b/docs/throttle.txt > @@ -1,6 +1,6 @@ > The QEMU throttling infrastructure > ================================== > -Copyright (C) 2016 Igalia, S.L. > +Copyright (C) 2016,2020 Igalia, S.L. > Author: Alberto Garcia > > This work is licensed under the terms of the GNU GPL, version 2 or > @@ -253,3 +253,108 @@ up. After those 60 seconds the bucket will have leaked 60 x 100 = > > Also, due to the way the algorithm works, longer burst can be done at > a lower I/O rate, e.g. 1000 IOPS during 120 seconds. > + > + > +The 'throttle' block filter > +--------------------------- > +Since QEMU 2.11 it is possible to configure the I/O limits using a > +'throttle' block filter. This filter uses the exact same throttling > +infrastructure described above but can be used anywhere in the node > +graph, allowing for more flexibility. > + > +The user can create an arbitrary number of filters and each one of > +them must be assigned to a group that contains the actual I/O limits. > +Different filters can use the same group so the limits are shared as > +described earlier in "Applying I/O limits to groups of disks". > + > +A group can be created using the object-add QMP function: > + > + { "execute": "object-add", > + "arguments": { > + "qom-type": "throttle-group", > + "id": "group0", > + "props": { > + "limits" : { > + "iops-total": 1000 > + "bps-write": 2097152 > + } > + } > + } > + } > + > +throttle-group has a 'limits' property (of type ThrottleLimits as > +defined in qapi/block-core.json) which can be set on creation or later > +with 'qom-set'. > + > +A throttle-group can also be created with the -object command line > +option but at the moment there is no way to pass a 'limits' parameter > +that contains a ThrottleLimits structure. The solution is to set the > +individual values directly, like in this example: > + > + -object throttle-group,id=group0,x-iops-total=1000,x-bps-write=2097152 > + > +Note however that this not stable API (hence the 'x-' prefixes) and > +can change or disappear in the future. Should we use a stronger wording here, like "will disappear when -object gains support for structured options and enables use of 'limits'"? > +Once we have a throttle-group we can use the throttle block filter, > +where the 'file' property must be set to the block device that we want > +to filter: > + > + { "execute": "blockdev-add", > + "arguments": { > + "options": { > + "driver": "qcow2", > + "node-name": "disk0", > + "file": { > + "driver": "file", > + "filename": "/path/to/disk.qcow2" > + } > + } > + } > + } > + > + { "execute": "blockdev-add", > + "arguments": { > + "driver": "throttle", > + "node-name": "throttle0", > + "throttle-group": "group0", > + "file": "disk0" > + } > + } > + > +A similar setup can also be done with the command line, for example: > + > + -drive driver=throttle,throttle-group=group0, > + file.driver=qcow2,file.file.filename=/path/to/disk.qcow2 > + > +The scenario described so far is very simple but the throttle block > +filter allows for more complex configurations. For example, let's say > +that we have three different drives and we want to set I/O limits for > +each one of them and an additional set of limits for the combined I/O > +of all three drives. > + > +First we would define all throttle groups, one for each one of the > +drives and one that would apply to all of them: > + > + -object throttle-group,id=limits0,x-iops-total=2000 > + -object throttle-group,id=limits1,x-iops-total=2500 > + -object throttle-group,id=limits2,x-iops-total=3000 > + -object throttle-group,id=limits012,x-iops-total=4000 > + > +Now we can define the drives, and for each one of them we use two > +chained throttle filters: the drive's own filter and the combined > +filter. > + > + -drive driver=throttle,throttle-group=limits012, > + file.driver=throttle,file.throttle-group=limits0 > + file.file.driver=qcow2,file.file.file.filename=/path/to/disk0.qcow2 > + -drive driver=throttle,throttle-group=limits012, > + file.driver=throttle,file.throttle-group=limits1 > + file.file.driver=qcow2,file.file.file.filename=/path/to/disk1.qcow2 > + -drive driver=throttle,throttle-group=limits012, > + file.driver=throttle,file.throttle-group=limits2 > + file.file.driver=qcow2,file.file.file.filename=/path/to/disk2.qcow2 > + > +In this example the individual drives have IOPS limits of 2000, 2500 > +and 3000 respectively but the total combined I/O can never exceed 4000 > +IOPS. Reviewed-by: Kevin Wolf Depending on whether you want to change the sentence about the unstable interface, I'll wait for v2 or merge this one. Kevin