From: Ingo Molnar <mingo@elte.hu>
To: Erich Focht <efocht@ess.nec.de>
Cc: "Martin J. Bligh" <mbligh@aracnet.com>,
Christoph Hellwig <hch@infradead.org>,
Robert Love <rml@tech9.net>,
Michael Hohnbaum <hohnbaum@us.ibm.com>,
Andrew Theurer <habanero@us.ibm.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
lse-tech <lse-tech@lists.sourceforge.net>,
Linus Torvalds <torvalds@transmeta.com>
Subject: Re: [PATCH 2.5.58] new NUMA scheduler: fix
Date: Fri, 17 Jan 2003 15:07:51 +0100 (CET) [thread overview]
Message-ID: <Pine.LNX.4.44.0301171459430.9021-100000@localhost.localdomain> (raw)
In-Reply-To: <200301171210.03567.efocht@ess.nec.de>
On Fri, 17 Jan 2003, Erich Focht wrote:
> I prefer a single point of entry called load_balance() to multiple
> functionally different balancers. [...]
agreed - my cleanup patch keeps that property.
> [...] IIRC, his conclusion for the multi-queue scheduler was that an
> order of magnitude of 10ms is long enough, below you start feeling the
> balancing overhead, above you waste useful cycles.
this is one reason why we do the idle rebalancing at 1 msec granularity
right now.
> On a NUMA system this is even more important: the longer you leave fresh
> tasks on an overloaded node, the more probable it is that they allocate
> their memory there. And then they will run with poor performance on the
> node which stayed idle for 200-400ms before stealing them. So one wastes
> 200-400ms on each CPU of the idle node and at the end gets tasks which
> perform poorly, anyway. If the tasks are "old", at least we didn't waste
> too much time beeing idle. The long-term target should be that the tasks
> should remember where their memory is and return to that node.
i'd much rather vote for fork() and exec() time 'pre-balancing' and then
making it quite hard to move a task across nodes.
> > The inter-node balancing (which is heavier than even the global SMP
> > balancer), should never be triggered from the high-frequency path.
>
> Hmmm, we made it really slim. [...]
this is a misunderstanding. I'm not worried about the algorithmic overhead
_at all_, i'm worried about the effect of too frequent balancing - tasks
being moved between runqueues too often. That has shown to be a problem on
SMP. The prev_load type of statistic measurement relies on a constant
frequency - it can lead to over-balancing if it's called too often.
> So if the CPU is idle, it won't go through schedule(), except we get an
> interrupt from time to time... [...]
(no, it's even better than that, we never leave the idle loop except when
we _know_ that there is scheduling work to be done. Hence the
need_resched() test. But i'm not worried about balancing overhead at all.)
Ingo
next prev parent reply other threads:[~2003-01-17 13:54 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-01-09 23:54 Minature NUMA scheduler Martin J. Bligh
2003-01-10 5:36 ` [Lse-tech] " Michael Hohnbaum
2003-01-10 16:34 ` Erich Focht
2003-01-10 16:57 ` Martin J. Bligh
2003-01-12 23:35 ` Erich Focht
2003-01-12 23:55 ` NUMA scheduler 2nd approach Erich Focht
2003-01-13 8:02 ` Christoph Hellwig
2003-01-13 11:32 ` Erich Focht
2003-01-13 15:26 ` [Lse-tech] " Christoph Hellwig
2003-01-13 15:46 ` Erich Focht
2003-01-13 19:03 ` Michael Hohnbaum
2003-01-14 1:23 ` Michael Hohnbaum
2003-01-14 4:45 ` [Lse-tech] " Andrew Theurer
2003-01-14 4:56 ` Martin J. Bligh
2003-01-14 11:14 ` Erich Focht
2003-01-14 15:55 ` [PATCH 2.5.58] new NUMA scheduler Erich Focht
2003-01-14 16:07 ` [Lse-tech] " Christoph Hellwig
2003-01-14 16:23 ` [PATCH 2.5.58] new NUMA scheduler: fix Erich Focht
2003-01-14 16:43 ` Erich Focht
2003-01-14 19:02 ` Michael Hohnbaum
2003-01-14 21:56 ` [Lse-tech] " Michael Hohnbaum
2003-01-15 15:10 ` Erich Focht
2003-01-16 0:14 ` Michael Hohnbaum
2003-01-16 6:05 ` Martin J. Bligh
2003-01-16 16:47 ` Erich Focht
2003-01-16 18:07 ` Robert Love
2003-01-16 18:48 ` Martin J. Bligh
2003-01-16 19:07 ` Ingo Molnar
2003-01-16 18:59 ` Martin J. Bligh
2003-01-16 19:10 ` Christoph Hellwig
2003-01-16 19:44 ` Ingo Molnar
2003-01-16 19:43 ` Martin J. Bligh
2003-01-16 20:19 ` Ingo Molnar
2003-01-16 20:29 ` [Lse-tech] " Rick Lindsley
2003-01-16 23:31 ` Martin J. Bligh
2003-01-17 7:23 ` Ingo Molnar
2003-01-17 8:47 ` [patch] sched-2.5.59-A2 Ingo Molnar
2003-01-17 14:35 ` Erich Focht
2003-01-17 15:11 ` Ingo Molnar
2003-01-17 15:30 ` Erich Focht
2003-01-17 16:58 ` Martin J. Bligh
2003-01-18 20:54 ` NUMA sched -> pooling scheduler (inc HT) Martin J. Bligh
2003-01-18 21:34 ` [Lse-tech] " Martin J. Bligh
2003-01-19 0:13 ` Andrew Theurer
2003-01-17 18:19 ` [patch] sched-2.5.59-A2 Michael Hohnbaum
2003-01-18 7:08 ` William Lee Irwin III
2003-01-18 8:12 ` Martin J. Bligh
2003-01-18 8:16 ` William Lee Irwin III
2003-01-19 4:22 ` William Lee Irwin III
2003-01-17 17:21 ` Martin J. Bligh
2003-01-17 17:23 ` Martin J. Bligh
2003-01-17 18:11 ` Erich Focht
2003-01-17 19:04 ` Martin J. Bligh
2003-01-17 19:26 ` [Lse-tech] " Martin J. Bligh
2003-01-18 0:13 ` Michael Hohnbaum
2003-01-18 13:31 ` [patch] tunable rebalance rates for sched-2.5.59-B0 Erich Focht
2003-01-18 23:09 ` [patch] sched-2.5.59-A2 Erich Focht
2003-01-20 9:28 ` Ingo Molnar
2003-01-20 12:07 ` Erich Focht
2003-01-20 16:56 ` Ingo Molnar
2003-01-20 17:04 ` Ingo Molnar
2003-01-20 17:10 ` Martin J. Bligh
2003-01-20 17:24 ` Ingo Molnar
2003-01-20 19:13 ` Andrew Theurer
2003-01-20 19:33 ` Martin J. Bligh
2003-01-20 19:52 ` Andrew Theurer
2003-01-20 19:52 ` Martin J. Bligh
2003-01-20 21:18 ` [patch] HT scheduler, sched-2.5.59-D7 Ingo Molnar
2003-01-20 22:28 ` Andrew Morton
2003-01-21 1:11 ` Michael Hohnbaum
2003-01-22 3:15 ` Michael Hohnbaum
2003-01-22 16:41 ` Andrew Theurer
2003-01-22 16:17 ` Martin J. Bligh
2003-01-22 16:20 ` Andrew Theurer
2003-01-22 16:35 ` Michael Hohnbaum
2003-02-03 18:23 ` [patch] HT scheduler, sched-2.5.59-E2 Ingo Molnar
2003-02-03 20:47 ` Robert Love
2003-02-04 9:31 ` Erich Focht
2003-01-20 17:04 ` [patch] sched-2.5.59-A2 Martin J. Bligh
2003-01-21 17:44 ` Erich Focht
2003-01-20 16:23 ` Martin J. Bligh
2003-01-20 16:59 ` Ingo Molnar
2003-01-17 23:09 ` Matthew Dobson
2003-01-16 23:45 ` [PATCH 2.5.58] new NUMA scheduler: fix Michael Hohnbaum
2003-01-17 11:10 ` Erich Focht
2003-01-17 14:07 ` Ingo Molnar [this message]
2003-01-16 19:44 ` John Bradford
2003-01-14 16:51 ` Christoph Hellwig
2003-01-15 0:05 ` Michael Hohnbaum
2003-01-15 7:47 ` Martin J. Bligh
2003-01-14 5:50 ` [Lse-tech] Re: NUMA scheduler 2nd approach Michael Hohnbaum
2003-01-14 16:52 ` Andrew Theurer
2003-01-14 15:13 ` Erich Focht
2003-01-14 10:56 ` Erich Focht
2003-01-11 14:43 ` [Lse-tech] Minature NUMA scheduler Bill Davidsen
2003-01-12 23:24 ` Erich Focht
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