From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2D4ECC35679 for ; Mon, 24 Feb 2020 10:00:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0B8AC20828 for ; Mon, 24 Feb 2020 10:00:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727378AbgBXJ77 (ORCPT ); Mon, 24 Feb 2020 04:59:59 -0500 Received: from foss.arm.com ([217.140.110.172]:34728 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726509AbgBXJ77 (ORCPT ); Mon, 24 Feb 2020 04:59:59 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1930C30E; Mon, 24 Feb 2020 01:59:59 -0800 (PST) Received: from [10.37.12.155] (unknown [10.37.12.155]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9E8D63F703; Mon, 24 Feb 2020 01:59:57 -0800 (PST) Subject: Re: [RFC PATCH v2 07/13] firmware: arm_scmi: Add notification dispatch and delivery From: Lukasz Luba To: Cristian Marussi , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: sudeep.holla@arm.com, james.quinlan@broadcom.com, Jonathan.Cameron@Huawei.com References: <20200214153535.32046-1-cristian.marussi@arm.com> <20200214153535.32046-8-cristian.marussi@arm.com> Message-ID: Date: Mon, 24 Feb 2020 09:59:55 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2/21/20 7:11 PM, Lukasz Luba wrote: > > > On 2/21/20 7:01 PM, Cristian Marussi wrote: >> Hi Lukasz >> >> Thanks for your feedback ! >> >> On 21/02/2020 13:25, Lukasz Luba wrote: >>> Hi Cristian, >>> >>> I didn't want to jump into your discussion with Jim in other broader >>> thread with this small thought, so I added a comment below. >>> >>> On 2/14/20 3:35 PM, Cristian Marussi wrote: >>>> Add core SCMI Notifications dispatch and delivery support logic >>>> which is >>> [snip] >>> >>>> @@ -840,6 +1071,11 @@ static struct scmi_notify_ops notify_ops = { >>>>     */ >>>>    int scmi_notification_init(struct scmi_handle *handle) >>>>    { >>>> +    scmi_notify_wq = alloc_workqueue("scmi_notify", >>>> +                     WQ_UNBOUND | WQ_FREEZABLE, 0); >>> >>> I think it might limit some platforms. It depends on their workload. >>> If they have some high priority workloads which rely on this mechanisms, >>> they might need a RT task here. The workqueues would be scheduled in >>> CFS, so it depends on workload in there (we might even see 10s ms delays >>> in scheduling-up them). If we use RT we would grab the CPU from CFS. >>> >>> It would be good if it is a customization option: which mechanism >>> to use based on some a parameter. Then we could create: >>> a) workqueue with the flags above >>> b) workqueue with WQ_HIGHPRI (limited by minimum nice) >>> c) kthread_create_worker() with RT/DL/FIFO sched policy >>>     (with also a parameterized priority) >>> In default clients might use a) but when they want to tune their >>> platform, they might change only a parameter in their scmi code, >>> not maintaining a patch for the RT function out of tree. >> >> In this series, I have not addressed configurability issues at all (as >> noted in the cover): >> in fact I was thinking that stuff like WQ_HIGHPRI flags and >> per-protocol queue sizes could >> be beneficial to be customizable depending on the specific platform, >> but I had not gone to >> the extreme of thinking of adopting a dedicated RT kthread as a >> worker...good point...it >> makes surely sense to have this configurable option to try to reduce >> the latency where possible. >> >> I think it's important to give the user the possibility to configure >> the deferred worker >> as you suggested, if the user decides to rely on Linux to handle a >> critical notification, >> but I'd prefer queuing up this work you suggested on a different >> series on top of this one. >> (which is starting to be a little to much voluminous...for being just >> the core support) > > Agree, you can build these features incrementally. Although, a WQ_SYSFS flag wouldn't harm too much this version and might give possibility to tune/experiment with it. > > Regards, > Lukasz >