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LWN.net Weekly Edition for May 23, 2013
An "enum" for Python 3
An unexpected perf feature
LWN.net Weekly Edition for May 16, 2013
A look at the PyPy 2.0 release
"Configure your kernel with 1000Hz, preempt ON and disable dynamic ticks."
It says "lower spec"
Posted Sep 1, 2009 18:34 UTC (Tue) by drag (subscriber, #31333)
Until the Linux kernel gets everything all situated out I think one of the big things that distros can probably do to improve user experience is provide Desktop/Multimedia optimized kernels.
Normally I am a big fan of 'do one thing and get it right before worrying about features' approach, but it's irritating to have to recompile my kernel to get proper responsiveness because the kernels from Debian are all optimized for server use.
$ grep -i preempt /boot/config-2.6.*
/boot/config-2.6.26-2-686:# CONFIG_PREEMPT_VOLUNTARY is not set
/boot/config-2.6.26-2-686:# CONFIG_PREEMPT is not set
/boot/config-2.6.30-1-686:# CONFIG_PREEMPT_RCU is not set
/boot/config-2.6.30-1-686:# CONFIG_PREEMPT_RCU_TRACE is not set
/boot/config-2.6.30-1-686:# CONFIG_PREEMPT_VOLUNTARY is not set
/boot/config-2.6.30-1-686:# CONFIG_PREEMPT is not set
I mean, seriously.. How long has Preempt support been around? *cry*
Posted Sep 1, 2009 22:30 UTC (Tue) by cortana (subscriber, #24596)
Posted Sep 2, 2009 1:54 UTC (Wed) by N0NB (guest, #3407)
Desktop Debian = Ubuntu
Posted Sep 2, 2009 4:55 UTC (Wed) by zlynx (subscriber, #2285)
Posted Sep 2, 2009 5:43 UTC (Wed) by jordanb (guest, #45668)
Posted Sep 2, 2009 7:39 UTC (Wed) by patrick_g (subscriber, #44470)
Posted Sep 2, 2009 13:00 UTC (Wed) by nye (guest, #51576)
Desktop Debian rocks
Posted Sep 2, 2009 8:32 UTC (Wed) by man_ls (subscriber, #15091)
You might say that these are servers being admin'd graphically. Let us see typically desktop-y applications: quick browsing shows regular users of Firefox (iceweasel really) at 33%, libgstreamer at 27%, evince at 26%, libgphoto2 and openoffice both at 25%. To put these figures in perspective, Apache is at 44% and Samba at 27%.
There are lots of bias in the sample: only utter geeks would install popularity-contest, and only properly connected machines will show up. I would counter that both things pretty much describe Debian's audience. IMHO saying that 50% of Debian users have it as a desktop is a good estimation.
Posted Sep 2, 2009 11:54 UTC (Wed) by N0NB (guest, #3407)
Posted Sep 2, 2009 20:41 UTC (Wed) by branden (subscriber, #7029)
Nice to meet you. I'm Branden.
Posted Sep 2, 2009 20:47 UTC (Wed) by zlynx (subscriber, #2285)
I mean, when I said it, I meant people I actually know in person and I know what they're running.
Now, as I don't make a habit of going around asking people if they're running Ubuntu or Debian or what, my sample size is about 5 people.
One of those I know used to run a Debian laptop and I *think* he is running Ubuntu now but possibly not. I know the other 4 are running Ubuntu.
Posted Sep 2, 2009 21:01 UTC (Wed) by alex (subscriber, #1355)
Posted Sep 3, 2009 13:10 UTC (Thu) by nix (subscriber, #2304)
(of course I'm running Debian on the desktop too, and adminning it remotely for my mum, who's in the same boat, and all she wants is something that Just Works and isn't virally infestable...)
Posted Sep 2, 2009 9:45 UTC (Wed) by cortana (subscriber, #24596)
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=311185 -- as of 2007, more testing for stability required; 'realtime patch' also mentioned, I have no idea if that still exists for current kernels or whether it's been merged
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=496871 -- request for benchmarks (along with "please stop waffling", great way to interact with users, kernel team...)
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=539209 -- filed recently (July 09) but no reply
Does anyone actually have any benchmarks demonstrating the efficacy of the pre-emption options?
Posted Sep 2, 2009 16:57 UTC (Wed) by drag (subscriber, #31333)
Technically a preemptive kernel will be slower then a non-preemptive one in most complex benchmarks. This is because going from process to process rapidly means more context changes and thus you lose out on cpu memory cache and all that.
But since the desktop is idle 99% of the time then it's easy to make the justification that it's worth it to say "Ya it takes a couple milliseconds longer to open a webpage, but this way I can do it without getting my music interrupted or keep my game/movie framerate high."
Intel developed a tool called latencytop that can be used to identify processes that are hogging the system and can causing usability or deterministic time problems.
Remember the point to having 'realtime' performance is not to make things _faster_ per say.. it's to make things more deterministic. So you know how long it will take to get something done. On a very hard-ish realtime system you can say "It's going to take a maximum of 30msec to accomplish X task" and you can depend on it. On a typical Linux server system it may take 5-10msec most of the time to do the same amount of work, but if something else is going on then it may take 500msec or more; You can't tell how long something is going to take, even though it's likely to get done faster on average.
This sort of trade off is what you need to keep your video smooth, games fast, music interrupt free, scientific measurements accurate, robotic assembly machines from zapping the wrong parts of a chassis, etc etc. Anytime you need to interact with the real world....
So ya.. benchmarks are very difficult and are skirting the issue.
Posted Sep 2, 2009 13:41 UTC (Wed) by guus (subscriber, #41608)
"THESE ARE OPTIONAL FOR LOWEST LATENCY. YOU DO NOT NEED THESE!"
So with tickless kernels, you get a slightly less low latency, but it would work fine.
Posted Sep 2, 2009 15:12 UTC (Wed) by rsidd (subscriber, #2582)
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