linux-kernel - Re: + sched-use-tasklet-to-call-balancing.patch added to -mm tree

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Message-ID: <20061107203147.GB4753@elte.hu>
Date:	Tue, 7 Nov 2006 21:31:47 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <clameter@....com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>, akpm@...l.org,
	mm-commits@...r.kernel.org, nickpiggin@...oo.com.au,
	linux-kernel@...r.kernel.org
Subject: Re: + sched-use-tasklet-to-call-balancing.patch added to -mm tree


* Christoph Lameter <clameter@....com> wrote:

> Tasklets are scheduled on the same cpu that triggered the tasklet. 
> They are just moved to other processors if the processor goes down. So 
> that aspect is fine. We just need a tasklet struct per cpu.
> 
> User a per cpu tasklet to schedule rebalancing
> 
> Turns out that tasklets have a flag that only allows one instance to 
> run on all processors. So we need a tasklet structure for each 
> processor.

Per-CPU tasklets are equivalent to softirqs, with extra complexity and 
overhead ontop of it :-)

so please just introduce a rebalance softirq and attach the scheduling 
rebalance tick to it. But i'd suggest to re-test on the 4096-CPU box, 
maybe what 'fixed' your workload was the global serialization of the 
tasklet. With a per-CPU softirq approach we are i think back to the same 
situation that broke your system before.

	Ingo
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