** Tags added: cscc
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Title:
Ubuntu server uses CFQ scheduler instead of deadline
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In my opinion I also agree to use deadline scheduler for server kernel
which is also the same problem on the 4.15 kernel, if a server kernel
would still exist.
Under trusty we generally saw good performance with deadline scheduler and on a
recent SSD based deployment with 4.15 I noticed a large
I observe substantial lag under heavy I/O (in my case I was unzipping a
multigigabyte archive) with the deadline scheduler. Manually switching
to the cfq scheduler improved responsiveness and eliminated the lag.
Perhaps cfq is a better choice for the desktop version?
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BTW, that IBM article... it doesn't mention what versions they used,
which I think is very important :-(.
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Title:
Ubuntu server uses CFQ
In my humble opinion, several kernel options should be tested before each new
Ubuntu version to see what is the best one at the time.
This is one such option.
Isn't the CFQ scheduler in better shape in Ubuntu 14.04?
Maybe not, I am just asking :-).
Thanks for the info! :-)
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See also bug:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1064521
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Title:
Ubuntu server uses CFQ scheduler instead of deadline
To
Thanks for fixing this in Quantal! Deadline is the 'best' choice for
servers and computers with SSD's. However there are situations where CFQ
is preferred, like desktop PC's with a hard drive. But I can imagine it
isn't easy to detect this in a reliable way.
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Well the obvious downside of deadline is that priorities (ionice) are
not supported.
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Title:
Ubuntu server uses CFQ scheduler instead of
We (Ubuntu kernel team) have been evaluating CFQ vs deadline. For this
specific bug report, we need some hard facts to make a decision about
changing to deadline IO scheduler. For example, any test case or
sequence we can reproduce easily.
Here is comparison of CFQ vs Deadline
We (Ubuntu kernel team) have been evaluating CFQ vs deadline. For this
specific bug report, we need some hard facts to make a decision about
changing to deadline IO scheduler. For example, any test case or
sequence we can reproduce easily.
Here is comparison of CFQ vs Deadline
Hark,
We've changed default IO scheduler from CFQ to deadline for both server
and desktop kernel. Please find our latest kernel from git tree for
Quantal release, any test and bug report are welcome.
Thanks,
-Bryan
** Changed in: linux (Ubuntu)
Status: Confirmed = In Progress
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Hi Bryan,
Thanks for taking this seriously. I only have the testcase I described above.
This server is now in production, so I cannot do any more tests on it.
However it should be easy to test the performance of deadline vs CFQ on a
server, and lots of people did this and wrote about it on
Hark,
We (Ubuntu kernel team) have been evaluating CFQ vs deadline. For this
specific bug report, we need some hard facts to make a decision about
changing to deadline IO scheduler. For example, any test case or
sequence we can reproduce easily.
Do you have such simple test case sharing with us?
As Andy said the wrong scheduler decision should worst case result in
worse performance. But getting so bad that a kvm guest sees disk
failures is more than should be allowed. It would be good if we could
reproduce this. For that it would be good to know more about the setup:
For the host:
- What
For the host:
-We use a md RAID indeed, raid 1
-The host and the guest both use ext4. On the host the file system is on a LVM
LV indeed
For the guest:
-The virtual disk is in a qcow2 image file
-At first we used an emulated IDE disk. We have now changed this to virtio, but
this was done a few
Thanks for the detailed info. I agree that disk starvation should not happen.
Though it could be that deadline just about covers some other problem. There
are a few pieces that add to slow down the host io, the RAID1 and the qcow2
file image. Using the IDE emulation would actually slow down the
Thinking about it the IDE emulation may be the problem. If I remember it
well the disk timeout messages on the guest had 'ata' in it. This is not
really my cup of tea but I know that ATA and IDE are related.
But please remember that my problem is only one example of what can
happen when using CFQ
@Andy - The logs that could be interesting are the logs of the virtual
server (kvm). However I don't have this log anymore, as I had to replace
the kvm image with a backup because of this problem. But let me try to
explain the situation, you'll see that unfairness is not the issue here.
- I
@Hark -- though the default is changed we would not expect hangs from
using CFQ, or are we just talking about gross unfairness. Can you share
the logs of the failures.
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Yes Leann and Bryan, I can boot with elevator=deadline and that is
exactly what I did after I noticed that CFQ was being used. But this
remains a bug that should be solved. Most people don't even know what a
scheduler is, or how to change it. On a server it is almost always a bad
idea to use CFQ.
I believe you can boot with elevator=deadline to switch back to the
Deadline I/O Scheduler.
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Title:
Ubuntu server uses CFQ scheduler instead of
I tried install latest Ubuntu Server image on my machine and confirmed
that we are using CFQ for default IO scheduler for both server and
desktop now.
Hark, we merged -server and -generic kernel image together for easier
maintenance and most difference can be switched via kernel command line
or
** Package changed: linux-meta (Ubuntu) = linux (Ubuntu)
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Title:
Ubuntu server uses CFQ scheduler instead of deadline
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Log files are completely irrelevant for this issue.
** Changed in: linux (Ubuntu)
Status: Incomplete = Confirmed
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Title:
Ubuntu server
** Changed in: linux (Ubuntu)
Assignee: (unassigned) = Bryan Wu (cooloney)
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Title:
Ubuntu server uses CFQ scheduler instead of deadline
To
** Changed in: linux (Ubuntu)
Importance: Undecided = Medium
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Title:
Ubuntu server uses CFQ scheduler instead of deadline
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