If ext4lazyinit isn't in used, do we still see the performance
regression?
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https://bugs.launchpad.net/bugs/1880943
Title:
[focal] disk I/O performance regression
To manage
Playing around with the now available IO schedulers does not appear to
help much and looking at iotop while the test runs does show
ext4lazyinit consuming much of the IO most of the time while the test
runs.
I wonder if this is a more ominous change of behavior after all
Total DISK READ:
We have been using the ext4lazyinit for quite some time, so I guess this
must be a combination of multiple things.
I see that the 5.4 kernel brings a change of io scheduler to mq-
deadline.
Could the combination of ext4lazyinit+mq-deadline+rotational drives be a
problem?
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For any future travelers this issue was caused by the much debated
ext4lazyinit "feature".
# iotop
Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s
Current DISK READ: 0.00 B/s | Current DISK WRITE: 7.38 M/s
TID PRIO USER DISK READ DISK WRITE SWAPIN
That is an excellent idea.
Before embarking on that endeavor I did a last control test which
involved deploying Bionic and then installing the Focal 5.4 kernel
packages, and lo and behold the system is still performant.
Redeploying Focal (with the Focal kernel obviously) makes it non-
performant
Would it be possible for you to do a kernel bisection?
First, find the last -rc kernel works and the first -rc kernel doesn’t
work from http://kernel.ubuntu.com/~kernel-ppa/mainline/
Then,
$ sudo apt build-dep linux
$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
$
Thank you for the suggestion to test mainline.
Regarding the kernel parameters: The test is run on the host and not in
a virtual machine, for completeness I have removed the iommu and vf
related kernel parameters and they do not affect the outcome of the
test.
Unfortunately using the mainline
Note that I didn't add any kernel parameter, so my first guess would be
"iommu=pt" doesn't get passthrough right.
** Changed in: linux (Ubuntu)
Status: Confirmed => Incomplete
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Tried 4.15.0-102, 5.4.0-33 and mailing kernel all three show similar
performance (~2100MB/s).
Please test latest mainline kernel:
https://kernel.ubuntu.com/~kernel-ppa/mainline/v5.7-rc7/
And decide what's the next step based on the performance of mainline
kernel.
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Note that to rule out any hardware configuration/malfunction issue
between the two hosts I have re-run the tests on the exact same machine
used for the non-performant Focal tests with good performance for
Bionic.
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** Tags added: uosci
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https://bugs.launchpad.net/bugs/1880943
Title:
[focal] disk I/O performance regression
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