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Date: Tue, 29 Jan 2008 13:30:04 +0100 From: Peter Zijlstra <a.p.zijlstra@...llo.nl> To: Paul Jackson <pj@....com> Cc: linux-kernel@...r.kernel.org, mingo@...e.hu, vatsa@...ux.vnet.ibm.com, dhaval@...ux.vnet.ibm.com, nickpiggin@...oo.com.au, ebiederm@...ssion.com, akpm@...ux-foundation.org, sgrubb@...hat.com, rostedt@...dmis.org, ghaskins@...ell.com, dmitry.adamushko@...il.com, tong.n.li@...el.com, tglx@...utronix.de, menage@...gle.com, rientjes@...gle.com Subject: Re: scheduler scalability - cgroups, cpusets and load-balancing On Tue, 2008-01-29 at 06:03 -0600, Paul Jackson wrote: > Paul, responding to Peter: > > > We now have a per-cpuset Boolean flag file called 'sched_load_balance'. > > > > SD_LOAD_BALANCE, right? > > No. SD_LOAD_BALANCE is some attribute of sched domains. > > The 'sched_load_balance' flag is an attribute of cpusets. > > The mapping of cpusets to sched domains required several pages of 'fun > to write' code, which had to go through a couple of years of fixing and > one major rewrite before it (knock on wood) worked correctly. It's not > a one-to-one relation, in other words. See my earlier messages for > further explanation of how this works. Ok, I'll take a stab at understanding that code. Perhaps it seems to me a lot of confusion could be solved by getting a more level playing ground :-) > > > This 'sched_load_balance' flag is, thus far, "the" cpuset hook > > > supporting realtime. One can use it to configure a system so that > > > the kernel does not do normal load balancing on select CPUs, such > > > as those CPUs dedicated to realtime use. > > > > Ah, here I disagree, it is possible to do (hard) realtime scheduling > > over multiple cpus, the only draw back is that it requires a very strong > > load-balancer, making it unsuitable for large number of cpus. > > I don't think we are disagreeing. I was speaking of "normal" > load balancing (what the mainline kernel/sched.c code normally > does). You're speaking of hard realtime load balancing. > > I think we agree that these both exist, and require different > load balancing code, the latter 'very strong.' Great :-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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