From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752285AbcFNPiz (ORCPT ); Tue, 14 Jun 2016 11:38:55 -0400 Received: from mail-wm0-f41.google.com ([74.125.82.41]:37837 "EHLO mail-wm0-f41.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752106AbcFNPix (ORCPT ); Tue, 14 Jun 2016 11:38:53 -0400 Subject: Re: [PATCH V4] irq: Track the interrupt timings To: Nicolas Pitre References: <1460545556-15085-1-git-send-email-daniel.lezcano@linaro.org> <57600866.4070601@linaro.org> Cc: Thomas Gleixner , shreyas@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, peterz@infradead.org, rafael@kernel.org, vincent.guittot@linaro.org From: Daniel Lezcano Message-ID: <57602506.1020007@linaro.org> Date: Tue, 14 Jun 2016 17:38:46 +0200 User-Agent: Mozilla/5.0 (X11; Linux i686; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/14/2016 05:10 PM, Nicolas Pitre wrote: > On Tue, 14 Jun 2016, Daniel Lezcano wrote: > >> On 06/10/2016 04:52 PM, Thomas Gleixner wrote: >> >>>> + timings->sum -= timings->values[timings->w_index]; >>>> + timings->values[timings->w_index] = diff; >>>> + timings->sum += diff; >>> >>> Now the real question is whether you really need all that math, checks and >>> memsets in the irq hotpath. If you make the storage slightly larger then you >>> can just store the values unconditionally in the circular buffer and do all >>> the computational stuff when you really it. >> >> Yes, that was one concern when I wrote the code: do some basic computation >> when an interrupt occurs, and the rest after or do the entire math when >> entering idle. >> >> If the storage is a bit larger (let's say 16 values) and there is no memset >> and the sum is not computed, at least we need a count for the number of values >> in the array before this one is fulfilled, otherwise the statistics will be >> wrong as we will take into account the entire array with old values, no ? > > The point is not to change from 8 to 16 entries, but to store raw 64-bit > timestamps instead of computed 32-bit deltas. Whether or not those > timestamps are too far apart and discarded can be done at idle entry > time. Ah, ok. That makes sense. Thanks for the clarification. -- Daniel -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog