/srv/irclogs.ubuntu.com/2016/08/19/#ubuntu-kernel.txt

jsheerenhi there09:03
jsheerenquick question about running the cloudimages on an openstack platform and specificaly io performance differences between stock xenial and stock trusty with a xenial-lts kernel installed through apt09:04
jsheerenare there differences in the kernel options?09:04
jsheerenthe xenial cloud image with kernel 4.4.0-24-generic has almost 2 times better IO performance than the trusty cloud image with the xenial-lts 4.4.0-34-generic kernel09:06
jsheerenwhich i find surprising as i would expect the same performance09:06
mdeslaurjsheeren: just a theory, but the xenial kernel is built with a newer gcc12:56
mdeslaur5.4.0 vs 4.8.412:58
xnoxbetter/newer userspace too? (depending on how the testing is done....)12:58
mdeslaurthat too12:58
jsheerenso the xenial kernel for xenial is built with 5.4.0, the xenial kernel for trusty is built with 4.8.4?12:59
mdeslauryep13:00
xnoxjsheeren, the package for each release is built in the target release build chroot. So all of toolchain for -lts kernels is from the target distro. Everything including things like binutils, glibc, compilers, etc.13:01
xnoxthe backport kernels are just that -> new source code, new package name, compiled on an old release.13:02
jsheerenjust to add hardware compatibility, but not to enhance performance, etc?13:02
xnoxit's not a .deb / binary copy. (that would result in naming clash)13:02
jsheerenis it doable to upgrade the gcc on trusty to the version on xenial?  or are there too many dependencies that will bork?13:03
xnoxjsheeren, there are multiple reasons and multiple usecases as to why hwe kernels were started to be provided. It's a mix of hardware compat / performance / (new)security features13:03
xnoxno no no no13:03
xnoxthat would break the ABI13:03
xnoxon c++13:03
jsheerenok13:03
xnoxi mean kernel is special, cause it's stand-alone / freestanding code.13:04
xnoxbut we would not do that.... Upgrade to xenial perhaps? =)13:04
xnoxit is shiny =)13:04
mdeslaurit's got the "new car" scent13:05
jsheerenxnox: yeah if we run a do-release-upgrade on trusty so we end up with a xenial, the performance issue is the same13:06
jsheerenwe've looked at a lot of stuff13:06
jsheerenusing the same hypervisor, same openstack flavor, etc13:06
jsheerena bit stumped at the moment on why we are seeing the IO performance difference that is so large at the moment 13:06
jsheerenwe compared the sysctl settings as well but did not see any differences that would impact IO13:08
xnoxjsheeren, your findings would be interesting. To rule things out, you /could/ *warning not supported* enable xenail repository on trusty, pin it down below trusty with apt-pinning, install/upgrade generic kernel from the xenial repository with e.g. apt install linux-generic/xenial, see what happens.13:08
jsheerenah yeah, could try that13:08
xnoxthis way you will rule out if the $userspace in xenial affecting benchmarks, or indeed the 4.4 kernel compiled on xenial, when running trusty userspace, is better.13:08
jsheerenwe tried copying the files from a xenial to a trusty but that did not go so well ... heh13:08
xnoxyeah.... partial apt upgrade to xenial to get new kernel from xenial rather than via hwe-stack is *safer*. Still a frankenstein =)13:09
jsheerenhttps://gist.github.com/beci/2a2091f282042ed20cda   this is a no go then?13:10
=== Elimin8r is now known as Elimin8er
phillwI take it that the 9134 version is the latest.... Quite a step change from the last one?...22:49
phillwphillw@piglet:~$ ls -lt /boot/abi*22:49
phillw-rw-r--r-- 1 root root 1241623 Aug 16 23:23 /boot/abi-4.4.0-9134-generic22:49
phillw-rw-r--r-- 1 root root 1241623 Jul 27 22:28 /boot/abi-4.4.0-34-generic22:49
phillwKindest Regards,22:49
phillwPhill.22:49

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