Re: Inquiry: Should we remove "isolcpus= kernel boot option? (may have realtime uses)

[Dimitri Sivanich <sivanich@sgi.com>]

On Mon, Jun 02, 2008 at 11:39:34AM -0700, Max Krasnyansky wrote:
> Ah, I know exactly what you're talking about.  However this is non-issue these
> days. In order to clear cpuN from all the timers and other things all you need
> to do is to bring that cpu off-line
> 	echo 0 > /sys/devices/cpu/cpuN/online
> and then bring it back online
> 	echo 1 > /sys/devices/cpu/cpuN/online

Although it seemed like something of a hack, we experimented with this
previously and found that it didn't work reliably.  I'm sure things
have gotten better, but will need to revisit.

> 
> There are currently a couple of issues with scheduler domains and hotplug
> event handling. I do have the fix for them, and Paul had already acked it.

Until a proven reliable method for doing this is firmly in place (as
firmly as anything is, anyway),  I don't think we should be removing
the alternative.

> initialization). See my latest "default IRQ affinity" patch.

Nice idea.

> Also isolcpus= conflicts with the scheduler domains created by the cpusets.

What sort of conflict are we talking about?  I assume once you've begun setting up cpusets that include those cpus that you're intention is to change the original behavior.