linux-kernel - Re: [PATCH 4/5] powernv:idle: Move initialization of sibling pacas to pnv_alloc_idle_core

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Date:   Mon, 10 Jul 2017 14:34:08 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nicholas Piggin <npiggin@...il.com>,
        Gautham R Shenoy <ego@...ux.vnet.ibm.com>
Cc:     Michael Neuling <mikey@...ling.org>,
        Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
        Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Akshay Adiga <akshay.adiga@...ux.vnet.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH 4/5] powernv:idle: Move initialization of sibling pacas to pnv_alloc_idle_core_states

Nicholas Piggin <npiggin@...il.com> writes:
> On Fri, 7 Jul 2017 20:34:16 +0530
> Gautham R Shenoy <ego@...ux.vnet.ibm.com> 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.

cheers