Re: [PATCH 4/5] powernv:idle: Move initialization of sibling pacas to pnv_alloc_idle_core_states

From: Michael Ellerman
Date: Mon Jul 10 2017 - 00:35:10 EST

Nicholas Piggin <npiggin@xxxxxxxxx> writes:
> On Fri, 7 Jul 2017 20:34:16 +0530
> Gautham R Shenoy <ego@xxxxxxxxxxxxxxxxxx> wrote:
>> On Fri, Jul 07, 2017 at 01:16:09AM +1000, Nicholas Piggin wrote:
>> >
>> > Speaking of which... core_idle_state and thread_sibling_pacas are
>> > allocated with kmalloc_node... What happens if we take an SLB miss
>> > in the idle wakeup code on these guys? Nothing good I think. Perhaps
>> > we should put them into the pacas or somewhere in bolted memory.
>> Yes, though the SLB miss hasn't yet been encountered in practise so
>> far!
> Considering it's a node-affine allocation, it may actually be possible
> to hit in practice on very large memory systems in practice.

You can boot with disable_1tb_segments on the kernel command line to
increase the change of hitting it.