Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753157AbbKQMxn (ORCPT ); Tue, 17 Nov 2015 07:53:43 -0500 Received: from smtprelay4.synopsys.com ([198.182.47.9]:36659 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750969AbbKQMxl (ORCPT ); Tue, 17 Nov 2015 07:53:41 -0500 Subject: NMI for ARC To: Peter Zijlstra References: <1445286926.3913.13.camel@synopsys.com> <20151117110749.GT3816@twins.programming.kicks-ass.net> <564B0E18.3040207@synopsys.com> <20151117122401.GY3816@twins.programming.kicks-ass.net> <20151117122540.GL11639@twins.programming.kicks-ass.net> CC: arcml , Alexey Brodkin , lkml Newsgroups: gmane.linux.kernel.arc,gmane.linux.kernel From: Vineet Gupta Message-ID: <564B2341.4030409@synopsys.com> Date: Tue, 17 Nov 2015 18:23:21 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151117122540.GL11639@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.12.197.182] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1554 Lines: 35 On Tuesday 17 November 2015 05:55 PM, Peter Zijlstra wrote: > This is assuming you now have these NMIs we talked about earlier. If all > you have are regular IRQs this is not possible, for we should be calling > ->read() with IRQs disabled. > No we don't yet. The first stab at it fell flat on floor. The NMI support from hardware is that is it provides different priorities, higher one obviously able to interrupt lower one. However instructions like CLRI (disable interrupts) will still lock out all interrupts. Thus local_irq_save()/restore() and local_irq_enable()/disable() now need to be contextual. - When running in prio 0 mode, they only need to enable 0 - In prio 1, they need to enable both 0 and 1 For irq_save()/restore() this is achievable by doing an additional STATUS32 read at the time of save and passing that value to restore - so there's an additional overhead - but ignoring that for now. Bummer is irq_disable()/enable() case: there's need to pass old prio state from enable to disabled, so we need some sort of global state tracking - which in case of SMP needs to be per cpu.... either keep something hot in a reg or pay the cost of additional mem/cache line miss. I've not investigated how other arches do that. PPC seems to be using some sort of soft irq state anyways. -- 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/