3.18-rc6

[zika]

http://kernel.ubuntu.com/~kernel-ppa....18-rc6-vivid/

[Ian_Worrall]

There seems to be a regression since RC4 that causes "lock-ups". Kernel bisection is ongoing.

http://lkml.iu.edu/hypermail/linux/k...1.2/05503.html

[Doug S]

I never did get around to trying 3.18RC5. Kernel 3.18RC6 seems to be working fine for me, but I haven't done much with it yet.

[Doug S]

It seems I can no longer change the scheduler or view which one I m currently using. Does anybody know when this changed?
Example from my older 12.04 server:

doug@doug-64:~$ uname -a
Linux doug-64 3.2.0-70-generic #105-Ubuntu SMP Wed Sep 24 19:49:16 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
doug@doug-64:~$ cat /sys/block/sda/queue/scheduler
noop deadline [cfq]

Example from my test server running 14.04:

doug@s15:~/temp2$ uname -a
Linux s15 3.13.0-40-generic #69-Ubuntu SMP Thu Nov 13 17:53:56 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
doug@s15:~/temp2$ cat /sys/block/sda/queue/scheduler
noop [deadline] cfq

Example from my test server running 14.04 and kernel 3.18RC6:

doug@s15:~$ uname -a
Linux s15 3.18.0-031800rc6-generic #201411231935 SMP Mon Nov 24 00:36:20 UTC 2014 x86_64 x86_64 x86_64 GNU/Linux
doug@s15:~$ cat /sys/block/sda/queue/scheduler
none      <<< Huh?

As yet I haven't been able to figure out a kernel config file difference reason. These are the same in both:

# IO Schedulers
CONFIG_IOSCHED_NOOP=y
CONFIG_IOSCHED_DEADLINE=y
CONFIG_IOSCHED_CFQ=y
CONFIG_CFQ_GROUP_IOSCHED=y
CONFIG_DEFAULT_IOSCHED="deadline"

Edit 1: I have it narrowed down to being introduced between 3.18RC1 and 3.18RC2. Recall all the excitement with 3.18RC2, perhaps this is another issue.
Edit 2: Back on 3.18RC2, one test I did was:

Kernel 3.18RC2 Kernel.org version.
. Compiled using the Ubuntu config file from kernel 3.18RC1, and accepting defaults for new stuff.
. Boots fine. Seems to run fine, but haven't done much yet.

That kernel works fine in terms of showing and allowing me to change the scheduler:

doug@s15:~$ uname -a
Linux s15 3.18.0-rc2-250 #167 SMP Mon Oct 27 21:46:56 PDT 2014 x86_64 x86_64 x86_64 GNU/Linux
doug@s15:~$ cat /sys/block/sda/queue/scheduler
noop [deadline] cfq

I will now pick away at the config file changes in an attempt to isolate the one that gives the issue.

[fooman]

compiled my own, if that makes any difference....but seems to work here:

~$ uname -a
Linux GA-990FXA-UD5 3.18.0-rc6-foomans-custom-kernel #1 SMP Mon Nov 24 06:50:37 EST 2014 x86_64 x86_64 x86_64 GNU/Linux

~$ cat /sys/block/sda/queue/scheduler
noop [deadline] cfq

[Doug S]

The difference seems to be:

doug@s15:~/temp-k-git-3.10rc4/linux$ diff .config_3.18rc6_cfg04 .config_3.18rc6_250
1995c1995
< # CONFIG_SCSI_MQ_DEFAULT is not set
---
> CONFIG_SCSI_MQ_DEFAULT=y

@fooman: can you confirm or deny that your kernel config file contains:

# CONFIG_SCSI_MQ_DEFAULT is not set

[fooman]

The difference seems to be:

doug@s15:~/temp-k-git-3.10rc4/linux$ diff .config_3.18rc6_cfg04 .config_3.18rc6_250
1995c1995
< # CONFIG_SCSI_MQ_DEFAULT is not set
---
> CONFIG_SCSI_MQ_DEFAULT=y

@fooman: can you confirm or deny that your kernel config file contains:

# CONFIG_SCSI_MQ_DEFAULT is not set

confirmed Doug...it does indeed.

#
# SCSI device support
#
CONFIG_SCSI_MOD=y
# CONFIG_RAID_ATTRS is not set
CONFIG_SCSI=y
CONFIG_SCSI_DMA=y
# CONFIG_SCSI_NETLINK is not set
# CONFIG_SCSI_MQ_DEFAULT is not set
CONFIG_SCSI_PROC_FS=y

[Doug S]

The kernel configuration parameter, CONFIG_SCSI_MQ_DEFAULT, will be put back to "is not set" in the next upload. Reference.

[zika]

elevator=cfq

should work in kernel boot-line.
Update₁: No, it does not, even though I thought it would. Tested on 999 & 994.
Upsate₂: It works now, both in 999 and in 994. Both from kernel boot line and afterwards from CLI.

[Doug S]

elevator=cfq

should work in kernel boot-line.
Update₁: No, it does not, even though I thought it would. Tested on 999 & 994.
Upsate₂: It works now, both in 999 and in 994. Both from kernel boot line and afterwards from CLI.

I see that the daily build has the config file difference(s) added:

doug@s15:~/temp-k-git-3.10rc4/linux$ diff .config-3.18.0-031800rc6-generic .config-3.18.0-999-generic
3c3
< # Linux/x86_64 3.18.0-031800rc6-generic Kernel Configuration
---
> # Linux/x86_64 3.18.0-999-generic Kernel Configuration
1995c1995
< CONFIG_SCSI_MQ_DEFAULT=y
---
> # CONFIG_SCSI_MQ_DEFAULT is not set
7039c7039
< # CONFIG_OVERLAY_FS is not set
---
> CONFIG_OVERLAY_FS=m

Users with significant system load should not use Ubuntu Kernels 3.18RC2 - 3.18RC6, as things tend to fall apart when the load is high enough that IO scheduling is required. Why? Because there isn't any IO scheduler. At least if you are experiencing oddities and system lag under high loads, this is a possible explanation. For example, I had a simple "ls -l" command that didn't complete in over 1/2 an hour (I had extreme disk IO load going from several tasks at the time). Anyway, 3.18RC7 should be out in a day or two.