Re: [PATCH] Reorganise and then fixup the pseries cpu hotplug code

[Michael Ellerman <michael@ellerman.id.au>]

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On Sun, 2006-11-19 at 22:22 -0600, jschopp wrote:
> >>> +	/* Isolation and deallocation are definatly done by
> >>                                         ^^^^^^^^^
> >> typo
> 
> That word definitely gives me trouble.  I'd imagine the typo originated with me.

Yeah it's definitely a tricky one ;)

> >>
> >>> +	 * drslot_chrp_cpu.  If they were not they would be
> >>> +	 * done here.  Change isolate state to Isolate and
> >>> +	 * change allocation-state to Unusable.
> >>> +	 */
> >>> +	paca[cpu].cpu_start = 0;
> >> I can't figure out what the comment means with respect 
> >> to this code ... 
> > 
> > Me either. It's unchanged from the original merge of cpu hotplug:
> > http://kernel.org/git/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=commit;h=24c13f21f0a6abe07020a959990da2b134e6734f
> > http://kernel.org/git/?p=linux/kernel/git/torvalds/old-2.6-bkcvs.git;a=blobdiff;h=72144b6122f9336e7fa242e50b65b099df0cd72b;hp=f671515c0676e61064ae414273fa4546d0c04938;hb=24c13f21f0a6abe07020a959990da2b134e6734f;f=arch/ppc64/kernel/smp.c
> > 
> > Which carries the name of one Joel Schopp :)
> > 
> > Grepping the tree at that point finds no other mention of
> > drslot_chrp_cpu, so I think it's a stale comment - we should probably
> > just rip it out - Joel?
> 
> It might be clearer by saying "the userspace program drslot_chrp_cpu" or "isolation and 
> deallocation occur in userspace, so just stop the cpu.  If isolation and deallocation ever 
> move from userpace to kernel space they would go here".  On pseries dynamic partitioning 
> or cpu guard (the things that initiate a cpu hotplug) all call a userspace program drmgr, 
> which calls drslot_chrp_cpu, which then talks to the firmware to isolate and unallocate 
> (on remove, the opposite on add) after it has hotplug removed the cpu via the /sys 
> interface.  This allows the cpu to be reassigned to another partition.
> 
> At least that's what I remember from back then when we did it.  Though I don't think it's 
> changed any.  Feel free to make the comment more intelligible.

OK, it didn't occur to me that it was referring to userspace. I'll
change it to:

/*
 * Isolation and deallocation occur in userspace, so just stop the cpu.
 * If isolation and deallocation ever move from userpace to kernel space
 * we would do them here.
 */

Sound OK?

cheers

-- 
Michael Ellerman
OzLabs, IBM Australia Development Lab

wwweb: http://michael.ellerman.id.au
phone: +61 2 6212 1183 (tie line 70 21183)

We do not inherit the earth from our ancestors,
we borrow it from our children. - S.M.A.R.T Person

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