Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751445AbbEYWge (ORCPT ); Mon, 25 May 2015 18:36:34 -0400 Received: from foss.arm.com ([217.140.101.70]:48524 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750903AbbEYWgc convert rfc822-to-8bit (ORCPT ); Mon, 25 May 2015 18:36:32 -0400 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (1.0) Subject: Re: [RFC PATCH 2/2] arm64: Implement vmalloc based thread_info allocator From: Catalin Marinas X-Mailer: iPhone Mail (12F70) In-Reply-To: <5601369.jDWtB6nFJC@wuerfel> Date: Tue, 26 May 2015 01:36:29 +0300 Cc: Jungseok Lee , Catalin Marinas , "barami97@gmail.com" , Will Deacon , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-arm-kernel@lists.infradead.org" Content-Transfer-Encoding: 8BIT Message-Id: <1CD6E4BA-95AF-420C-8270-6AAF783B6F60@foss.arm.com> References: <1432483340-23157-1-git-send-email-jungseoklee85@gmail.com> <5601369.jDWtB6nFJC@wuerfel> To: Arnd Bergmann Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1615 Lines: 35 On 25 May 2015, at 23:29, Arnd Bergmann wrote: > On Monday 25 May 2015 19:47:15 Catalin Marinas wrote: >> On 25 May 2015, at 13:01, Jungseok Lee wrote: >>>> Could the stack size be reduced to 8KB perhaps? >>> >>> I guess probably not. >>> >>> A commit, 845ad05e, says that 8KB is not enough to cover SpecWeb benchmark. >> >> We could go back to 8KB stacks if we implement support for separate IRQ >> stack on arm64. It's not too complicated, we would have to use SP0 for (kernel) threads >> and SP1 for IRQ handlers. > > I think most architectures that see a lot of benchmarks have moved to > irqstacks at some point, that definitely sounds like a useful idea, > even if the implementation turns out to be a bit more tricky than > what you describe. Of course, it's more complicated than just setting up two stacks (but I'm away for a week and writing from a phone). We would need to deal with the initial per-CPU setup, rescheduling following an IRQ, CPU on following power management and maybe other issues. However, the architecture helps us a bit by allowing both SP0 and SP1 to be used at EL1. > There are a lot of workloads that would benefit from having lower > per-thread memory cost. If we keep the 16KB stack, is there any advantage in a separate IRQ one (assuming that we won't overflow 16KB)? Catalin-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/