qemu/docs/throttle.txt

11 QEMU includes a throttling module that can be used to set limits to
22 Two aspects of the disk I/O can be limited: the number of bytes per
24 them the user can set a global limit or separate limits for read and
27 I/O limits can be set using the throttling.* parameters of -drive, or
43 and for each case we can decide whether to have separate read and
45 iops-read nor iops-write can be set. The same applies to bps-total and
50 In its most basic usage, the user can add a drive to QEMU with a limit
55 We can do the same using QMP. In this case all these parameters are
75 an amount of I/O that can exceed the basic limit. Bursts are useful to
81 I/O they allow. These two can be configured separately for each one of
112 With this, the user can perform I/O on hd0.qcow2 at a rate of 2000
119 are not allowed. 'iops-total-max-length' can only be set if
145 regardless of their size. This means that the user can take advantage
212    - I/O limits can be disabled by setting all of them to 0. In this
236   - Water can be added to the bucket at a rate of 2000 IOPS.
243 The bucket is initially empty, therefore water can be added until it's
245 we can only add as much water as it leaks, therefore the I/O rate is
254 Also, due to the way the algorithm works, longer burst can be done at
262 infrastructure described above but can be used anywhere in the node
265 The user can create an arbitrary number of filters and each one of
267 Different filters can use the same group so the limits are shared as
270 A group can be created using the object-add QMP function:
284 defined in qapi/block-core.json) which can be set on creation or later
287 A throttle-group can also be created with the -object command line
298 Once we have a throttle-group we can use the throttle block filter,
324 A similar setup can also be done with the command line, for example:
343 Now we can define the drives, and for each one of them we use two
358 and 3000 respectively but the total combined I/O can never exceed 4000