--- Comment From dougm...@us.ibm.com 2018-08-06 09:43 EDT---
We are also seeing this behavior on Bionic 18.04.
I don't understand the request for better comments. The Launchpad
comments seem to include a fairly complete description of the problem.
Are there specific questions about this
--- Comment From frede...@fr.ibm.com 2018-07-31 13:10 EDT---
Doug,
- do we have patches for this issue ? I saw you talked about some but as I
understand they do not seem satisfactory.
- can any of the cfq tunables help on this ?
- if not, do we have some extended tests/view of deadline
--- Comment From dougm...@us.ibm.com 2018-07-16 09:02 EDT---
*** Bug 169550 has been marked as a duplicate of this bug. ***
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https://bugs.launchpad.net/bugs/1709889
--- Comment From dougm...@us.ibm.com 2017-08-23 12:13 EDT---
By the way, I would not classify this behavior I'm seeing as a performance
issue. There are hundreds of I/Os per second on each disk, and most of them are
being submitted right away. But a subset of those I/Os are getting
--- Comment From dougm...@us.ibm.com 2017-08-23 08:45 EDT---
I tried running 4.13-rc6 with "cfq" set as default scheduler. The problem is
even worse. I/O delays show up almost immediately. Many exceed the HTX
10-minute limit. It seems that CFQ is even more broken on the latest kernels.
--- Comment From dougm...@us.ibm.com 2017-08-22 09:22 EDT---
Can we get some answers as to why CFQ is the default scheduler? It seems like
the expedient fix is to change the default to "deadline".
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--- Comment From dougm...@us.ibm.com 2017-08-18 07:51 EDT---
Test results with the binary kernel package show the same symptoms, I/Os
getting delayed longer than 10 minutes. It seems that those three patches
together cause a regression of the "cfq-iosched: fix the delay of cfq_group's
--- Comment From dougm...@us.ibm.com 2017-08-17 15:03 EDT---
I have started a test run using the binary kernel proposed, and will see if
there is evidence of the problem. Results will be available tomorrow.
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--- Comment From dougm...@us.ibm.com 2017-08-17 08:42 EDT---
Those three patches, at least in the kernel I am running, actually make things
worse. The characteristics have changed, in what appears to be a general
slow-down of disk I/O (it took over 12 hours to hit the first set of sever
--- Comment From dougm...@us.ibm.com 2017-08-16 08:17 EDT---
Even with all three of those patches, I still am seeing delayed I/Os. The
pattern looks the same, but I will run for 12+ hours to collect more data. At
this point, though, I believe that "cfq" should not be the default
--- Comment From dougm...@us.ibm.com 2017-08-16 07:23 EDT---
Oh, there is no source code in the linux-source package. I will have to add
those patches to my own source - which won't exactly test your kernel.
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--- Comment From dougm...@us.ibm.com 2017-08-15 16:36 EDT---
I will start a test with that kernel tomorrow. I will be adding my debug code
to it, so that I can track delayed I/Os if they occur. I see you posted source
code, so I can do that easily.
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--- Comment From dougm...@us.ibm.com 2017-08-15 09:32 EDT---
I should also add that the data indicates there is an instability to the delay,
with the initial stalled I/Os maxing out at about 70 seconds, then the next
cycle (~10 hours later) and subsequent 2 shows max values in the 90-100
--- Comment From dougm...@us.ibm.com 2017-08-15 09:26 EDT---
Here is what I am observing, and what leads me to think that "cfq" may not
(yet) be a good choice for the default io-sched.
The test exerciser, HTX (https://github.com/open-power/HTX - POWER arch
only), causes stress on CFQ
--- Comment From dougm...@us.ibm.com 2017-08-14 10:33 EDT---
I am currently making a long test run to collect some data. It may be the case
that cfq delays actually increase over time, even with this fix. That may be
evidence that cfq is not a good default choice for I/O scheduler, but I
--- Comment From dougm...@us.ibm.com 2017-08-11 07:44 EDT---
Testing shows that this commit appears to fix the problem. After 20 hours, no
evidence of stalled I/Os.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5be6b75610cefd1e21b98a218211922c2feb6e08
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