On Fri, Jul 07, 2017 at 01:16:09AM +1000, Nicholas Piggin wrote:
> On Wed,  5 Jul 2017 22:08:15 +0530
> "Gautham R. Shenoy" <e...@linux.vnet.ibm.com> wrote:
> 
> > From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com>
> > 
> > On POWER9 DD1, in order to get around a hardware issue, we store in
> > every CPU thread's paca the paca pointers of all its siblings.
> > 
> > Move this code into pnv_alloc_idle_core_states() soon after the space
> > for saving the sibling pacas is allocated.
> > 
> > Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
> 
> > -   if (cpu_has_feature(CPU_FTR_POWER9_DD1)) {
> > -           int cpu;
> > -
> > -           pr_info("powernv: idle: Saving PACA pointers of all CPUs in 
> > their thread sibling PACA\n");
> > -           for_each_possible_cpu(cpu) {
> > -                   int base_cpu = cpu_first_thread_sibling(cpu);
> > -                   int idx = cpu_thread_in_core(cpu);
> > -                   int i;
> > -
> 
> You could move the thread_sibling_pacas allocation to here?
> 
> 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!

While one can define thread_sibling_pacas in PACA, it doesn't make
sense to allocate space for core_idle_state in PACA since the
allocated value of the secondary threads will never be used.

What is the right way to ensure that these allocations fall in the
bolted range ?

> 
> Good cleanup though.
> 
> Reviewed-by: Nicholas Piggin <npig...@gmail.com>
> 

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