On Thu, 19 Aug 2004, Robert Jordens wrote: > Package: wnpp > Severity: wishlist > > Hi debian-multimedia! > > Who is interested in packaging this? I can't do it because I only have > my powerpc to test on which voluntary-preempt is not yet available for. > I know Guenter already did realtime-lsm (hint..). Someone from Agnula?
Hmm, I probably won't find the time to package this. A kernel patch is quite different from a kernel module package. I agree, that it would be nice to have it though, especially if we could lobby it into the standard Debian kernel (not that I know what it would take to do that). Guenter > > Thanks. > > Robert. > > > Package name : kernel-patch-voluntary-preempt > Version : 2.6.8.1-P4 > Upstream Author : Ingo Molnar <[EMAIL PROTECTED]> > URL : http://people.redhat.com/mingo/voluntary-preempt/ > License : GPL > Description : lower kernel latency by voluntary preemption > > From <http://people.redhat.com/mingo/voluntary-preempt/>: > > as most of you are probably aware of it, there have been complaints on > lkml that the 2.6 kernel is not suitable for serious audio work due to > high scheduling latencies (e.g. the Jackit people complained). I took a > look at latencies and indeed 2.6.7 is pretty bad - latencies up to 50 msec > (!) can be easily triggered using common workloads, on fast 2GHz+ x86 > system - even when using the fully preemptible kernel! > > to solve this problem, Arjan van de Ven and I went over various kernel > functions to determine their preemptability and we re-created from > scratch a patch that is equivalent in performance to the 2.4 lowlatency > patches but is different in design, impact and approach: > > http://redhat.com/~mingo/voluntary-preempt/ > > (Note to kernel patch reviewers: the split voluntary_resched type of > APIs, the feature #ifdefs and runtime flags are temporary and were > only introduced to enable a easy benchmarking/comparisons. I'll split > this up into small pieces and drop the conditional stuff/ifdefs once > there's testing feedback and actual audio users had their say!) > > unlike the lowlatency patches, this patch doesn't add a lot of new > scheduling points to the source code, it rather reuses a rich but > currently inactive set of scheduling points that already exist in the > 2.6 tree: the might_sleep() debugging checks. Any code point that does > might_sleep() is in fact ready to sleep at that point. So the patch > activates these debugging checks to be scheduling points. This reduces > complexity and impact quite significantly. > > but even using these (over one hundred) might_sleep() points there were > still a number of latency sources in the kernel - we identified and > fixed them by hand, either via additional might_sleep() checks, or via > explicit rescheduling points. Sometimes lock-break was necessary as > well. > > as a practical goal, this patch aims to fix all latency sources that > generate higher than ~1 msec latencies. We'd love to learn about > workloads that still cause audio skipping even with this patch applied, > but i've been unable to generate any load that creates higher than 1msec > latencies. (not counting driver initialization routines.) > > this patch is also more configurable than the 2.4 lowlatency patches > were: there's a .config option to enable voluntary preemption, and there > are runtime /proc/sys knobs and boot-time flags to turn voluntary > preemption (CONFIG_VOLUNTARY_PREEMPT) and kernel preemption > (CONFIG_PREEMPT) on/off: > > # turn on/off voluntary preemption (if CONFIG_VOLUNTARY_PREEMPT) > echo 1 > /proc/sys/kernel/voluntary_preemption > echo 0 > /proc/sys/kernel/voluntary_preemption > > # turn on/off the preemptible kernel feature (if CONFIG_PREEMPT) > /proc/sys/kernel/kernel_preemption > /proc/sys/kernel/kernel_preemption > > the 'voluntary-preemption=0/1' and 'kernel-preemption=0/1' boot options > can be used to control these flags at boot-time. > > all 4 combinations make sense if both CONFIG_PREEMPT and > CONFIG_VOLUNTARY_PREEMPT are enabled - great for performance/latency > testing and comparisons. > > The stock 2.6 kernel is equivalent to: > > voluntary_preemption:0 kernel_preemption:0 > > the 2.6 kernel with voluntary kernel preemption is equivalent to: > > voluntary_preemption:1 kernel_preemption:0 > > the 2.6 kernel with preemptible kernel enabled is: > > voluntary_preemption:0 kernel_preemption:1 > > and the preemptible kernel enhanced with additional lock-breaks is > enabled via: > > voluntary_preemption:1 kernel_preemption:1 > > it is safe to change these flags anytime. > > The patch is against 2.6.7-bk20, and it also includes fixes for kernel > bugs that were uncovered while developing this patch. While it works for > me, be careful when using this patch! > > Testreports, comments, suggestions are more than welcome, > > Ingo > > -- System Information: > Debian Release: 3.1 > APT prefers testing > APT policy: (990, 'testing'), (300, 'unstable') > Architecture: powerpc (ppc) > Kernel: Linux 2.6.8-rj1 > Locale: LANG=en_US.UTF-8, LC_CTYPE=en_US.UTF-8 > > -- > WYSIWYG: > What You See Is What You Get. >
