Bug 886044
Summary: | throttling IO on qemu-kvm lead to bad IO BPS in windows guests | ||
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Product: | Red Hat Enterprise Linux 7 | Reporter: | juzhang <juzhang> |
Component: | qemu-kvm | Assignee: | Stefan Hajnoczi <stefanha> |
Status: | CLOSED WONTFIX | QA Contact: | Virtualization Bugs <virt-bugs> |
Severity: | medium | Docs Contact: | |
Priority: | medium | ||
Version: | 7.0 | CC: | juzhang, knoel, kwolf, michen, qzhang, virt-maint |
Target Milestone: | rc | ||
Target Release: | --- | ||
Hardware: | Unspecified | ||
OS: | Unspecified | ||
Whiteboard: | |||
Fixed In Version: | Doc Type: | Bug Fix | |
Doc Text: | Story Points: | --- | |
Clone Of: | Environment: | ||
Last Closed: | 2013-03-28 16:17:32 UTC | Type: | Bug |
Regression: | --- | Mount Type: | --- |
Documentation: | --- | CRM: | |
Verified Versions: | Category: | --- | |
oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
Cloudforms Team: | --- | Target Upstream Version: | |
Embargoed: |
Description
juzhang
2012-12-11 11:54:22 UTC
Additional infos. 1. For linux guests, I tested as well. For the details, please refer to bz885681. 2. I tested ide disk as well under the same environment, The BPS is 259KB/s. From KVM QE POV, the actual result much bigger or smaller than specifying value are not acceptable. The result is expected behavior and has to do with the granularity of disk I/O requests. You are running fio with blocksize 1 MB. The guest OS breaks down the 1 MB into small requests but they are probably ~256 KB each. Since your bps limit is 512000, it is not possible to fit 2 256 KB requests. The result is that you only get around 259 KB per second. Please change the fio blocksize to 4 KB and retest. You should see that we get much closer to the bps limit. Alternatively, raise the limit so that a single I/O request is only a small fraction of the bps limit. |