VirtualBox

Ticket #14982 (closed defect: fixed)

Opened 19 months ago

Last modified 11 months ago

VBoxManage bandwidthctl breaks on low values => fixed in SVN/next maintenance

Reported by: dimaqq Owned by:
Priority: major Component: virtual disk
Version: VirtualBox 5.0.12 Keywords:
Cc: Guest type: other
Host type: other

Description

Setting disk bandwidth to a really low value (e.g. 1K) appears to turn off the throttle entirely, and throttle can only be re-enabled by vm power cycle (reboot is not enough).

Test: echo 3 > /proc/sys/vm/drop_caches time dd if=/dev/sdb of=/dev/null bs=1M count=10

Setup: Cloned a VM Set up IO group with 10M limit Attached existing 2nd SCSI disk to group

Test sequence: set limit to 1M booted up vm test result 1.2 MB/s repeated test (to be sure) test result 1.2 MB/s

set limit to 1K test result 91.9 MB/s

set limit to 1M test result 156 MB/s repeated test test result 82.0 MB/s

rebooted vm test result 82.0 MB/s

shut down vm started vm test resut 1.2 MB/s

Summary: It doesn't matter if low limit was set at runtime or in advance Critical value is between 210K (broken) and 225K (works) VM shutdown is needed to recover throttling

Attachments

VBox.log Download (310.6 KB) - added by dimaqq 19 months ago.

Change History

Changed 19 months ago by dimaqq

comment:1 Changed 12 months ago by aeichner

  • Summary changed from VBoxManage bandwidthctl breaks on low values to VBoxManage bandwidthctl breaks on low values => fixed in SVN/next maintenance

Thanks for the report, this will be fixed in the next maintenance release.

You will observe a somewhat higher throughput for really low values because VBox will process at least one I/O request from the guest per second, even if the request size is bigger than the limit to avoid stalling I/O completely.

You might also see more throughput for certain disk images because VBox limits only real reads/writes to the image, reading from an image with unallocated or compressed blocks will result in higher throughput in the guest.

comment:2 Changed 11 months ago by frank

  • Status changed from new to closed
  • Resolution set to fixed

Fix is part of 5.1.4.

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