SCHED_ULE should not be the default
freebsd at jdc.parodius.com
Thu Dec 15 02:42:53 UTC 2011
On Thu, Dec 15, 2011 at 03:05:12AM +0100, Oliver Pinter wrote:
> On 12/15/11, O. Hartmann <ohartman at zedat.fu-berlin.de> wrote:
> > On 12/14/11 18:54, Tom Evans wrote:
> >> On Wed, Dec 14, 2011 at 11:06 AM, George Mitchell
> >> <george+freebsd at m5p.com> wrote:
> >>> Dear Secret Masters of FreeBSD: Can we have a decision on whether to
> >>> change back to SCHED_4BSD while SCHED_ULE gets properly fixed?
> >> Please do not do this. This thread has shown that ULE performs poorly
> >> in very specific scenarios where the server is loaded with NCPU+1 CPU
> >> bound processes, and brought forward more complaints about
> >> interactivity in X (I've never noticed this, and use a FreeBSD desktop
> >> daily).
> > I would highly appreciate a decission against SCHED_ULE as the default
> > scheduler! SCHED_4BSD is considered a more mature entity and obviously
> > it seems that SCHED_ULE needs some refinements to achieve a better level
> > of quality.
> >> On the other hand, we have very many benchmarks showing how poorly
> >> 4BSD scales on things like postgresql. We get much more load out of
> >> our 8.1 ULE DB and web servers than we do out of our 7.0 ones. It's
> >> easy to look at what you do and say "well, what suits my environment
> >> is clearly the best default", but I think there are probably more
> >> users typically running IO bound processes than CPU bound processes.
> > You compare SCHED_ULE on FBSD 8.1 with SCHED_4BSD on FBSD 7.0? Shouldn't
> > you compare SCHED_ULE and SCHED_4BSD on the very same platform?
> > Development of SCHED_ULE has been focused very much on DB like
> > PostgreSQL, no wonder the performance benefit. But this is also a very
> > specific scneario where SCHED_ULE shows a real benefit compared to
> > SCHED_4BSD.
> >> I believe the correct thing to do is to put some extra documentation
> >> into the handbook about scheduler choice, noting the potential issues
> >> with loading NCPU+1 CPU bound processes. Perhaps making it easier to
> >> switch scheduler would also help?
> > Many people more experst in the issue than myself revealed some issues
> > in the code of both SCHED_ULE and even SCHED_4BSD. It would be a pitty
> > if all the discussions get flushed away like a "toilette-busisness" as
> > it has been done all the way in the past.
> > Well, I'd like to see a kind of "standardized" benchmark. Like on
> > openbenchmark.org or at phoronix.com. I know that Phoronix' way of
> > performing benchmarks is questionable and do not reveal much of the
> > issues, but it is better than nothing. I'm always surprised by the worse
> > performance of FreeBSD when it comes to threaded I/O. The differences
> > between Linux and FreeBSD of the same development maturity are
> > tremendous and scaring!
> > It is a long time since I saw a SPEC benchmark on a FreeBSD driven HPC
> > box. Most benchmark around for testing hardware are performed with Linux
> > and Linux seems to make the race in nearly every scenario. It would be
> > highly appreciable and interesting to see how Linux and FreeBSD would
> > perform in SPEC on the same hardware platform. This is only an idea.
> > Without a suitable benchmark with a codebase understood the discussion
> > is in many aspects pointless -both ways.
> >> Cheers
> >> Tom
> >> References:
> >> http://people.freebsd.org/~kris/scaling/mysql-freebsd.png
> >> http://suckit.blog.hu/2009/10/05/freebsd_8_is_it_worth_to_upgrade
> >> _______________________________________________
> Can you try with this settings:
> op at opn ~> sysctl kern.sched.
I'm replying with a list of each setting which differs compared to
RELENG_8 stock on our ULE systems. Note that our ULE systems are 1
physical CPU with 4 cores.
> kern.sched.cpusetsize: 8
I see no such tunable/sysctl on any of our RELENG_8 and RELENG_7
systems. Nor do I find any references to it in /usr/src (on any
system). Is this a RELENG_9 setting? Please explain where it comes
from. I hope it's not a custom kernel patch...
> kern.sched.preemption: 0
This differs; default value is 1.
> kern.sched.name: ULE
> kern.sched.slice: 13
> kern.sched.interact: 30
> kern.sched.preempt_thresh: 224
This differs; default value is 64. The "magic value" of 224 has been
discussed in the past, in this thread even.
> kern.sched.static_boost: 152
This differs; on our systems it's 160.
> kern.sched.idlespins: 10000
> kern.sched.idlespinthresh: 16
This differs; on our systems it's 4.
> Most of them from 7-STABLE settings, and with this, "works for me".
> This an laptop with core2 duo cpu (with enabled powerd), and my kernel
> config is here:
| Jeremy Chadwick jdc at parodius.com |
| Parodius Networking http://www.parodius.com/ |
| UNIX Systems Administrator Mountain View, CA, US |
| Making life hard for others since 1977. PGP 4BD6C0CB |
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