Bug 527916 - [Regression] xen HVM *and* KVM fsync performance for file-backed fs is very poor
Summary: [Regression] xen HVM *and* KVM fsync performance for file-backed fs is very poor
Alias: None
Product: Red Hat Enterprise Linux 5
Classification: Red Hat
Component: kernel
Version: 5.4
Hardware: All
OS: Linux
Target Milestone: rc
: ---
Assignee: Red Hat Kernel Manager
QA Contact: Red Hat Kernel QE team
Depends On:
Blocks: 526945 527917
TreeView+ depends on / blocked
Reported: 2009-10-08 08:36 UTC by Paolo Bonzini
Modified: 2016-04-26 15:18 UTC (History)
11 users (show)

Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Clone Of: 526945
Last Closed: 2010-01-28 18:05:39 UTC
Target Upstream Version:

Attachments (Terms of Use)

Comment 1 Paolo Bonzini 2009-10-12 18:03:34 UTC
Here are results from running the benchmark with various kernels, while keeping xen at xen-3.0.3-96.el5:

 host kernel    guest kernel   files/sec    app overhead
 166xen         (not virt)     139.1        163551
 166xen         166xen         31.6         89855
 166xen         155xen         49.7         83991
 162xen         (not virt)     137.1        163551
 162xen         166xen         31.8         91714
 162xen         155xen         34.1         86513
 155xen         (not virt)     113.3        175644
 155xen         166xen         32.0         131550
 155xen         155xen         48.8         84895

All numbers from "fs_mark -d test -d test2 -s 51200 -n 4096", running on 1 VCPU for virtualized, and 4 VCPUs for bare metal.  The numbers are decently reproducible, but not perfectly, and they are quite weird.  So I'd say they're at best non-conclusive.  At most they hint that 166xen is not faster than 155xen. :-/  They also say that (more or less...) the host kernel is not relevant.

Important for anyone that wants to reproduce e.g. under KVM: if you use the same VM with different kernel versions, remember to drop caches (echo 3 > /proc/sys/vm/drop_caches) on the guest _and especially on the host_.

Comment 2 Ric Wheeler 2009-12-17 19:19:12 UTC
What kind of storage are you using? If this is on a local SAS class drive, the lower numbers are definitely more realistic. The 138 files/sec might be an indication that the write barrier code is not working properly?

Comment 3 Paolo Bonzini 2010-01-28 18:05:39 UTC
Since the KVM bug was closed, and the Xen bug is not in the kernel, closing.

Note You need to log in before you can comment on or make changes to this bug.