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

From: Ingo Molnar
Date: Tue Nov 07 2006 - 15:33:05 EST



* Christoph Lameter <clameter@xxxxxxx> 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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