Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753272AbbGFOWg (ORCPT ); Mon, 6 Jul 2015 10:22:36 -0400 Received: from mail-ob0-f173.google.com ([209.85.214.173]:35527 "EHLO mail-ob0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750765AbbGFOWe (ORCPT ); Mon, 6 Jul 2015 10:22:34 -0400 MIME-Version: 1.0 In-Reply-To: <20150706140503.GJ3644@twins.programming.kicks-ass.net> References: <1436189569-28802-1-git-send-email-jcmvbkbc@gmail.com> <1436189569-28802-8-git-send-email-jcmvbkbc@gmail.com> <20150706134708.GI3644@twins.programming.kicks-ass.net> <20150706140503.GJ3644@twins.programming.kicks-ass.net> Date: Mon, 6 Jul 2015 17:22:33 +0300 Message-ID: Subject: Re: [PATCH 7/8] xtensa: implement counting and sampling perf events From: Max Filippov To: Peter Zijlstra Cc: "linux-xtensa@linux-xtensa.org" , LKML , Chris Zankel , Marc Gauthier , Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2354 Lines: 57 On Mon, Jul 6, 2015 at 5:05 PM, Peter Zijlstra wrote: > On Mon, Jul 06, 2015 at 04:56:09PM +0300, Max Filippov wrote: >> On Mon, Jul 6, 2015 at 4:47 PM, Peter Zijlstra wrote: >> > On Mon, Jul 06, 2015 at 04:32:48PM +0300, Max Filippov wrote: >> >> +static int __init xtensa_pmu_init(void) >> >> +{ >> >> + int ret; >> >> + int irq = irq_create_mapping(NULL, XCHAL_PROFILING_INTERRUPT); >> > >> > Does this platform have interrupt priorities which you can partially >> > mask in order to create NMI like behaviour? >> >> Not sure what you mean by "NMI like". > > There's a number of archs where we implement NMIs by having > local_irq_disable() only disable part of the interrupt priority range > and making sure all 'normal' IRQs are mapped in that priority range. > > We then map our NMI handlers to a priority above the 'normal' range, > such that these interrupts can indeed happen when interrupts are > 'disabled. > > See for example: > > b4f4372f96e0 ("sparc64: Make %pil level 15 a pseudo-NMI.") > 0c25e9e6cbe7 ("sparc64: Adjust __raw_local_irq_save() to cooperate in NMIs.") > c011f80ba091 ("sparc64: Add some more commentary to __raw_local_irq_save()") Ok, I see. I guess I can change IRQ disabling logic to not mask perf IRQ in case it's configured as the only interrupt on its level and it's the highest medium-level IRQ. >> Interrupt priorities are fixed in the current xtensa architecture, and >> we can in theory mask certain level and below, but practically we >> always mask all low- and medium- level interrupts. >> >> Also we currently can't have handlers for high priority interrupts written in C. > > Why not? Surely this can be cured with an assembly stub? IIUC that was a deliberate architecture design choice and working around it penalizes all interrupt handlers. But let me take another close look. > The advantage of having NMIs is that profiling information for the > kernel becomes much more useful. Without this local_irq_enable() will be > a very 'hot' function. I haven't noticed that in my testing. -- Thanks. -- Max -- 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/