From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753622AbbIGOeY (ORCPT ); Mon, 7 Sep 2015 10:34:24 -0400 Received: from foss.arm.com ([217.140.101.70]:51131 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753546AbbIGOd7 (ORCPT ); Mon, 7 Sep 2015 10:33:59 -0400 Message-ID: <55EDA040.90208@arm.com> Date: Mon, 07 Sep 2015 15:33:36 +0100 From: James Morse User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Jungseok Lee CC: Catalin Marinas , Will Deacon , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC PATCH 0/3] Implement IRQ stack on ARM64 References: <1441376587-12979-1-git-send-email-jungseoklee85@gmail.com> In-Reply-To: <1441376587-12979-1-git-send-email-jungseoklee85@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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, 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. Thanks, James Morse