Date: Thu, 15 Dec 2011 08:41:10 +0100 From: Oliver Pinter <oliver.pntr@gmail.com> To: Jeremy Chadwick <freebsd@jdc.parodius.com> Cc: Tom Evans <tevans.uk@googlemail.com>, Attilio Rao <attilio@freebsd.org>, George Mitchell <george+freebsd@m5p.com>, "O. Hartmann" <ohartman@zedat.fu-berlin.de>, freebsd-stable@freebsd.org Subject: Re: SCHED_ULE should not be the default Message-ID: <CAPjTQNEPCk50JTx7KLiarT5W6N3UCov89uukpW2y0nKtmzfFyQ@mail.gmail.com> In-Reply-To: <20111215024249.GA13557@icarus.home.lan> References: <4EE1EAFE.3070408@m5p.com> <CAJ-FndDniGH8QoT=kUxOQ%2BzdVhWF0Z0NKLU0PGS-Gt=BK6noWw@mail.gmail.com> <4EE2AE64.9060802@m5p.com> <4EE88343.2050302@m5p.com> <CAFHbX1%2B5PttyZuNnYot8emTn_AWkABdJCvnpo5rcRxVXj0ypJA@mail.gmail.com> <4EE933C6.4020209@zedat.fu-berlin.de> <CAPjTQNEJDE17TLH-mDrG_-_Qa9R5N3mSeXSYYWtqz_DFidzYQw@mail.gmail.com> <20111215024249.GA13557@icarus.home.lan>
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On 12/15/11, Jeremy Chadwick <freebsd@jdc.parodius.com> wrote: > On Thu, Dec 15, 2011 at 03:05:12AM +0100, Oliver Pinter wrote: >> On 12/15/11, O. Hartmann <ohartman@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@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 >> >> _______________________________________________ >> >> Hi! >> >> Can you try with this settings: >> op@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. On other system that has 4 core I use 7-STABLE, because I have not enough time for upgraded it, and the system has some custom patches. The values what I send in previous mail mostly based on this 4 cores system. > >> 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... Yes, this is 9-STABLE. > >> kern.sched.preemption: 0 > > This differs; default value is 1. PREEMPTION is disabled via kernel config. > >> 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. This magic value has discussed before 1 or 1.5 year here, first for 8-STABLE. > >> 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: >> http://oliverp.teteny.bme.hu/freebsd/kernel_conf > > -- > | 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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