Mailinglist Archive: opensuse-features (202 mails)

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[openFATE 305694] Separate Desktop / Server Kernels
  • From: fate_noreply@xxxxxxx
  • Date: Wed, 1 Apr 2009 08:56:21 +0200 (CEST)
  • Message-id: <feature-305694-53@xxxxxxxxxxxxxx>
Feature changed by: De Ganseman Amaury (amaurydg)
Feature #305694, revision 53
Title: Separate Desktop / Server Kernels

openSUSE-11.2: Evaluation
Requester: Important
Projectmanager: Important

Requested by: Dean Hilkewich (deanjo13)

It seems to me that the current default kernels are somewhat hurting
openSUSE's performance perception. Current kernel configs are OK but
are not very well suited for desktop usage. In the future I would like
to see a kernel package that is optimized for desktop usage. Current
timer settings and no preemption really (sometimes drastically) hurts
openGL performance and applications such as wine and causes alot of
issues such as audio studdering. It would be nice to see a separate
desktop performance kernel package with options such as Preemption
model set to Preemptable Kenel (low-latency Desktop) and Timer
Frequency Set to 1000 Hz, HPET support, Tickless System, disable
optimize for size, disable Control Group support and disable Group CPU
scheduler. You could also disable items and modules that are extremely
rare in a desktop environment such as ATM support, Infiniband etc etc
as these are not typically used in a desktop scenario which would be a
large majority of openSUSE users. Further performance enhancements
would also be done through out the system aimed at desktop use as well
such as disabling barriers (even making it a simple checkmark option in
the partitioner). Such optimizations for desktop usage can overcome
openSUSE's reputation as being slower then the other mainstream
distro's. The kernel settings alone can make up to a 30-40% increase in
framerates in wine games for example and can cure alot of hiccups in
multimedia apps.

#1: Bernhard Friedreich (bernhard1234) (2009-01-18 15:25:11)
wow.. I didn't know about that facts.. I vote for that one! (running
both a server and multiple notebooks on openSUSE)

#2: Jan Engelhardt (jengelh) (2009-01-19 09:48:49)
So why do not you use the RT kernel if your problems are that bad?
Also, HPET and tickless is already enabled if you have not noticed. If
you suggest disabling Optimize For Size, then I disclaim that you know
all of the facts. A smaller kernel results in less instructions to
fetch and run, and as such, less execution time to complete a given
task. Unless you have specific numbers that an unloaded ATM module
slows down your daily operations, it is not going to go away just
because you think it is responsible for speed issues. Because as I read
the source, it seems to me that it merely introduces one test and
branch to the IPv4 ARP code, and that is just so small it is ridiculous
to debate about. I do however, would want to see the kernel package
being split up so as to have drivers that "probably are not" desktop-
related in this decade, like ATM, in a separate installable package.

#3: Dean Hilkewich (deanjo13) (2009-01-21 06:12:22)
Yes I realize that HPET and tickless are already in there by default.
I'm just pointing out settings that do make a difference for desktop
use. Optimize for Size (=Os) can in theory reduce the executable size
and can in some cases have small increases due to better cache usage,
however in real life practice on a desktop you will find that disabling
it (-02) does give a real life performance gain. Feel free to benchmark
on your own as well (BTW Grub starts looking pretty squished with tones
of kernels installed). These settings have been tested tried and true
in the mailing lists, forums, etc. The RT kernel still defaults to a
250 Hz timer, Control Group support and Group CPU. All of these hurt
multimedia and GL app performance. Easiest way of testing this for
yourself is put a demanding game in wine such as command and conquer 3
in wine and play it or try to play high def content on a system with
marginal system specs to do so. They make all the world of difference.
The reason I recommended removing ATM, Infniband etc etc etc for the
same reasons that you would like to see a separate kernel package for
little if ever used anymore modules.
I'm sure if you went through opensuse-help's own mailing list you can
see these configs mentioned more then a few times and the results they
give users afterwards.

#4: Dmitry Mittov (michael_knight) (2009-01-22 08:40:14)
How it will have impact to installation procces? Does user have to
choose kernel manually. Or it will be done automatically with help of
some criteria?

#7: Dean Hilkewich (deanjo13) (2009-01-23 02:26:22) (reply to #4)
It doesn't have to impact the installation process at all. What is
required to do this is just another .config kernel config file added to
the kernel src RPM and when that is built you would have a desktop
kernel. The process is really no different then the current kernel
choices we have now (rt, pae, default, xen etc). It doesn't even have
to really be hosted on the installation DVD/CD medium at all but could
be simply one of those extra packages just found on the full OSS
No separate installation images are needed but could be made if product
creator was massaged a bit more into a end user friendly app or once
susestudio goes live one could easily spin a custom dvd for their own
use. The key is to get these alternative kernel packages on the
official OSS repo.

#5: Vasiliy Astanin (madcad) (2009-01-22 17:49:21)
May be we should separate not only kernel, but entire images? openSUSE-
Desktop.iso contains KDE, Gnome and a lot of userspace software, but no
any Apaches, tomcat, or so. + it contains kernel-desktop openSUSE-
Server.iso contains no heavy DE, no OpenOffice, no any other large
desktop packages - only some extremely light WM - like icewm, but with
all server features. + it contains kernel-default, -server, or similar
Such splitted images will be much less in size, so maybe server will
even fit on CD. This way we'll get something similar to SLES/SLED, but
it may be a good tactics ;)

#6: Todd R (theblackcat) (2009-01-22 22:19:33)
Perhaps when someone is installing their system they can have a
selection of a few different pre-configured systems, such as
Desktop/Laptop and Server, and then an "Other" section that includes
Netbook, Text-only Desktop/Laptop, Text-only Server, Lightweight
Desktop/Laptop, Lightweight Server, Real-time System, Workstation, and
perhaps a few more advanced configurations that only advanced users
would want. Alternatively, you could ask when someone is first
installing the system "Are you planning to use this computer primarily
as a:" and they can pick either "Desktop/Laptop" or Server.
For established setups, having kernel-desktop and kernel-server
versions available in the software management could take care of
switching, but perhaps a generic Kernel Setup YaST module that allows
you to pick what sorts of things you want to serve as well as allowing
you to switch to the server kernel (or back) would help.

#8: Stephan Kleine (bitshuffler) (2009-02-23 21:05:37)
Apparently doing stuff like enabling PREEMPT and setting HZ to 1000
would not only result in a snappier system but also e.g. solve the
glitch problems with pulse audio:
(considering the amount of bitching about PA that alone should be a
good enough reason to do it ;D)
Even the kernel devs themself say, if I'm not completely mistaken, that
the one kernel for all approach isn't a good idea and that it makes
sense to have different flavors for -desktop & -server with their
settings tuned for the usecase.

#9: Stephan Kulow (coolo) (2009-02-24 11:05:04) (reply to #8)
Can't anyone of you check if they can get real data for the openSUSE
kernel config if changed like that?

#11: Karsten König (remur) (2009-02-24 17:15:40) (reply to #9)
maybe the kernel team could spin a -desktop kernel build for testing
and release it in kotd? This would make testing much easier then
building a custom one on our own systems and people could do test runs
with comparing them to each other.

#12: Stephan Kulow (coolo) (2009-02-25 11:54:31) (reply to #11)
well, I want to see numbers that are improved. Because we can simply
rename -default to -highperformance and people find it faster. It's
always the same story.

#14: Jeff Mahoney (jeff_mahoney) (2009-02-25 10:42:10) (reply to #12)
The thing is that this is an area where the "numbers" are subjective.
We currently make a trade-off between throughput and latency, where
throughput is preferred on the server environment. I've heard requests
from both sides of the fence - the server users don't want the overhead
of the preemption and the desktop users don't want to sacrifice a
responsive interactive experience to the server users.
This is something I thought about during a recent on-site. While I
won't commit to actually shipping separate kernels in the next release,
it's worth researching. I can tweak the configs in -master and see what
shakes out.
For testing, I'm inclined to split kernel-default (kernel-pae on i386)
into kernel-desktop and kernel-server. On i386, perhaps rename kernel-
default to kernel-legacy?

#15: Jeff Mahoney (jeff_mahoney) (2009-02-25 10:46:09) (reply to #14)
There are places where kernel-default is the expected name, though,
aren't there? Perhaps kernel-default = kernel-server, and kernel-
desktop, then.

#16: Stephan Kulow (coolo) (2009-02-26 10:01:43) (reply to #15)
Let's get Jiri in here, he should know the yast part. Others part that
require "kernel-default" should be pretty trivial to fix (the live cd
configs come to mind). But renaming our kernels sounds like a good
idea, that kernel-pae is installed by default confused many :)
Hmm - now that I think about that aspect: if we have a kernel-desktop,
then we need to have pae configurable at runtime first, or we'll have -
desktop the -pae and what's now -default will become -legacy. Then you
get kernel-server, kernel-legacy and kernel-desktop. But the live cds
would still need to stick with kernel-legacy. Damn. But possibly we can
have the updaters switch kernel flavors on first kernel update. Sounds
all solvable :)

#17: Jiri Srain (jsrain) (2009-02-26 14:45:48) (reply to #16)
YaST has some hardcoded options to select proper kernel, with fallbacks
(if the chosen does not exists). These will need to be adjusted, but
that's should be pretty trivial.
We will need a screen to select the role of the machine (we have
similar in SLES - server, virt. host, virt. guest); perhaps we should
also use this screen to preselect patterns - but that's just a side
effect of these changes). If we have such screen, preselecting the
right kernel will be easier.
Regarding the PAE vs. non-PAE kernel: We will install PAE kernel only
if the PAE flag is present && (machine has >3GB RAM || NX flag is
present), which will avoid the performance hit caused by PAE on
machines where it has no use.
I'd rather avoid hacking online update to replace legacy kernel with
PAE, it would IMO be quite tricky; since we have repos enabled on the
live media, replacing the kernel during media deployment should be a
safer solution.

#20: Karsten König (remur) (2009-02-27 11:40:00) (reply to #12)
Lennart Poettering added a alsa-time-test to pulseaudio to check
latency, would that be the kind of numbers you want to see? It is of
course only a single check for a very specific problem.

#21: Takashi Iwai (tiwai) (2009-02-27 11:57:23) (reply to #20)
No, it doesn't help in practice. The latency (responsiveness) can't be
measured in such a style because the situation that the test program
assumes (a tight busy loop) is completely different from the actual
situation where PA is running. It's a good tool to test how stable the
sound driver (hardware) is, though.

#18: Takashi Iwai (tiwai) (2009-02-26 15:05:14) (reply to #8)
Lennart's suggestion (HZ=1000 and CONFIG_PREEMPT) is nonsense. It won't
help the latency (for non-RT tasks) much. It rather consumes more power
and gets slower. His vocal opinion there is based on the very old data
or a placebo.
In general, the latency (or responsiveness) depends rather on the CPU
and IO schedulers. The RT-latency is a different story, and irrelevant
now as long as PA daemon is running as a normal task.
I find it's not bad to have a desktop kernel, though. The requirement
of the current scheduler and parameters are mostly for the server
performance (on SLES11), and they don't always fit with the desktop

#19: Jeff Mahoney (jeff_mahoney) (2009-02-26 09:19:24) (reply to #18)
Agreed. I had no intention of changing HZ=1000. Rather, I was going to
start by changing the preemption settings so that the desktop is super
aggressive about it, and back off the server configs.

#22: Jan Engelhardt (jengelh) (2009-03-01 16:44:23) (reply to #18)
However, HZ=100 (yes, 100, the old "server default") and
CONFIG_NO_PREEMPT=y does cause mplayer (non-RT app) to skip sometimes
during heavy load, such as `git status` in a Linux tree. So that
extreme of the two ends is also not too good ;-)

#10: andrea florio (anubisg1) (2009-02-24 11:26:47)
i agree with it, but please consider to keep PAE function enabled on
desktop kernel... most pc have 4GB ram, and if i install a 32bit system
i would like to use all my ram.

#13: Theodoros Nikolakopoulos (theodoros) (2009-02-25 16:24:49)
I agree, as far as there isn't any significant sacrifice on security
features from each.

#23: Dean Hilkewich (deanjo13) (2009-03-01 17:07:18)
I think it's important to keep in mind that a vast majority of openSUSE
users are desktop users. Even though openSUSE is used for the building
blocks for SLE where server usage is at a higher percentage, it's your
non-corporate desktop user that are the ones primarily using openSUSE.
Having separate desktop and server kernels allow you to cater to the
larger desktop community as well have a solution for the much smaller
server community. Lets face it when you see a review of openSUSE it's
almost always focused on the desktop usage and not on the server side.
That's where openSUSE's focus of improvement should be geared at.

#24: William Simon Lewis (williamsimonlewis) (2009-03-08 13:04:51)
Please correct me if I wrong but one advantage of having separate
installations for desktops and servers is that desktop users could have
noatime and nodiratime options set by default. According to Kerneltrap
this would bring a 10% speed increase in the journaling file systems on

#25: Dean Hilkewich (deanjo13) (2009-03-20 18:22:37)
William, this certainly could be done as well with a desktop profile.
(as well as disabling barriers as other desktop distributions do) but
kernel modification isn't needed to do that.

+ #26: De Ganseman Amaury (amaurydg) (2009-04-01 08:55:44)
+ I think it will be good if someone can do some "real life" benchmark to
+ sse if enable preempt or HZ=1000 or ..... can be a benefit for a
+ desktop.
+ Today the more annoying bug that cause VERY BIG latency is
+ and I don't see any
+ patches or fix on the lkml at the moment. This bug exist since 2.6.18
+ so...a lot of time !

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