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 <be...@igalia.com> > --- > 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 <be...@igalia.com> > > 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 <kw...@redhat.com> Depending on whether you want to change the sentence about the unstable interface, I'll wait for v2 or merge this one. Kevin