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qemu-options: explain disk I/O throttling options

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The disk I/O throttling options have been listed for a long time but
never explained on the QEMU man page.

Suggested-by: Nini Gu <ngu@redhat.com>
Cc: Alberto Garcia <berto@igalia.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-id: 20170301115026.22621-2-stefanha@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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Stefan Hajnoczi 2017-03-01 11:50:24 +00:00
parent fa54abb8c2
commit 01f9cfab8b
1 changed files with 24 additions and 0 deletions
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qemu-options.hx
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@ -635,6 +635,30 @@ file sectors into the image file.
conversion of plain zero writes by the OS to driver specific optimized conversion of plain zero writes by the OS to driver specific optimized
zero write commands. You may even choose "unmap" if @var{discard} is set zero write commands. You may even choose "unmap" if @var{discard} is set
to "unmap" to allow a zero write to be converted to an UNMAP operation. to "unmap" to allow a zero write to be converted to an UNMAP operation.
@item bps=@var{b},bps_rd=@var{r},bps_wr=@var{w}
Specify bandwidth throttling limits in bytes per second, either for all request
types or for reads or writes only. Small values can lead to timeouts or hangs
inside the guest. A safe minimum for disks is 2 MB/s.
@item bps_max=@var{bm},bps_rd_max=@var{rm},bps_wr_max=@var{wm}
Specify bursts in bytes per second, either for all request types or for reads
or writes only. Bursts allow the guest I/O to spike above the limit
temporarily.
@item iops=@var{i},iops_rd=@var{r},iops_wr=@var{w}
Specify request rate limits in requests per second, either for all request
types or for reads or writes only.
@item iops_max=@var{bm},iops_rd_max=@var{rm},iops_wr_max=@var{wm}
Specify bursts in requests per second, either for all request types or for reads
or writes only. Bursts allow the guest I/O to spike above the limit
temporarily.
@item iops_size=@var{is}
Let every @var{is} bytes of a request count as a new request for iops
throttling purposes. Use this option to prevent guests from circumventing iops
limits by sending fewer but larger requests.
@item group=@var{g}
Join a throttling quota group with given name @var{g}. All drives that are
members of the same group are accounted for together. Use this option to
prevent guests from circumventing throttling limits by using many small disks
instead of a single larger disk.
@end table @end table
By default, the @option{cache=writeback} mode is used. It will report data By default, the @option{cache=writeback} mode is used. It will report data