Re: [RFC PATCH 0/3] Implement IRQ stack on ARM64

[Jungseok Lee <jungseoklee85@gmail.com>]

On Sep 7, 2015, at 11:33 PM, James Morse wrote:
> On 04/09/15 15:23, Jungseok Lee wrote:
>> ARM64 kernel allocates 16KB kernel stack when creating a process. In case
>> of low memory platforms with tough workloads on userland, this order-2
>> allocation request reaches to memory pressure and performance degradation
>> simultaenously since VM page allocator falls into slowpath frequently,
>> which triggers page reclaim and compaction.
>> 
>> I believe that one of the best solutions is to reduce kernel stack size.
>> According to the following data from stack tracer with some fixes, [1],
>> a separate IRQ stack would greatly help to decrease a kernel stack depth.
>> 
> 
> Hi Jungseok Lee,

Hi James Morse,

> I was working on a similar patch for irq stack, (patch as a follow up email).
> 
> I suggest we work together on a single implementation. I think the only
> major difference is that you're using sp_el0 as a temporary register to
> store a copy of the stack-pointer to find struct thread_info, whereas I was
> copying it between stacks (ends up as 2x ldp/stps), which keeps the change
> restricted to irq_stack setup code.
> 
> We should get some feedback as to which approach is preferred.

Great idea!
I'd really like to figure out the most ideal implementation of this feature.

Best Regards
Jungseok Lee