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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS autolearn=ham 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 483ACC43381 for ; Thu, 14 Mar 2019 11:41:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 15D7720854 for ; Thu, 14 Mar 2019 11:41:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ti.com header.i=@ti.com header.b="we2TluHK" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727508AbfCNLlh (ORCPT ); Thu, 14 Mar 2019 07:41:37 -0400 Received: from fllv0015.ext.ti.com ([198.47.19.141]:57734 "EHLO fllv0015.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726829AbfCNLlg (ORCPT ); Thu, 14 Mar 2019 07:41:36 -0400 Received: from lelv0265.itg.ti.com ([10.180.67.224]) by fllv0015.ext.ti.com (8.15.2/8.15.2) with ESMTP id x2EBfTPi000599; Thu, 14 Mar 2019 06:41:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1552563689; bh=YievU1VLeC1+DrIa0xM6OPkS7VGiHM9hNIxkrSRAVV4=; h=Subject:To:CC:References:From:Date:In-Reply-To; b=we2TluHKtXdnIMT6sjh4w4S45lOidYitrnIugwZ9r6xaLeUwt+iN8wRrveJV7l0dV e3r1aIbzRA8JSphgz/Mj0G+HsK2GZ5rFL0T4rKlQUZ2oCrQVIJaD6ZgtQE0WgxdjVf UsdrKCnYeFRMHy3ybCnWZPuYm5dgzFPeBbAG2VD0= Received: from DFLE102.ent.ti.com (dfle102.ent.ti.com [10.64.6.23]) by lelv0265.itg.ti.com (8.15.2/8.15.2) with ESMTPS id x2EBfT8E086710 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 14 Mar 2019 06:41:29 -0500 Received: from DFLE104.ent.ti.com (10.64.6.25) by DFLE102.ent.ti.com (10.64.6.23) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1591.10; Thu, 14 Mar 2019 06:41:29 -0500 Received: from dflp33.itg.ti.com (10.64.6.16) by DFLE104.ent.ti.com (10.64.6.25) with Microsoft SMTP Server (version=TLS1_0, cipher=TLS_RSA_WITH_AES_256_CBC_SHA) id 15.1.1591.10 via Frontend Transport; Thu, 14 Mar 2019 06:41:29 -0500 Received: from [172.24.190.215] (ileax41-snat.itg.ti.com [10.172.224.153]) by dflp33.itg.ti.com (8.14.3/8.13.8) with ESMTP id x2EBfP1S025709; Thu, 14 Mar 2019 06:41:26 -0500 Subject: Re: [PATCH v2 1/8] mmc: sdhci: Get rid of finish_tasklet To: Grygorii Strashko , Adrian Hunter , , , , CC: , , , , References: <20190215192033.24203-1-faiz_abbas@ti.com> <20190215192033.24203-2-faiz_abbas@ti.com> <8d72ff93-e07f-52b9-da85-acd54f046694@ti.com> <63b6631d-86e7-b8ef-ffaf-40e7d4e96cfb@intel.com> <842caafd-1547-1ea6-faf0-27a85a912622@ti.com> <2a74ed21-2e6f-1ba3-3d49-6826a5ab3e66@ti.com> From: Faiz Abbas Message-ID: Date: Thu, 14 Mar 2019 17:11:21 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <2a74ed21-2e6f-1ba3-3d49-6826a5ab3e66@ti.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On 14/03/19 4:45 PM, Grygorii Strashko wrote: > > > On 12.03.19 19:30, Rizvi, Mohammad Faiz Abbas wrote: >> Hi Adrian, >> >> On 3/8/2019 7:06 PM, Adrian Hunter wrote: >>> On 6/03/19 12:00 PM, Faiz Abbas wrote: >>>> Adrian, >>>> >>>> On 25/02/19 1:47 PM, Adrian Hunter wrote: >>>>> On 15/02/19 9:20 PM, Faiz Abbas wrote: >>>>>> sdhci.c has two bottom halves implemented. A threaded_irq for handling >>>>>> card insert/remove operations and a tasklet for finishing mmc requests. >>>>>> With the addition of external dma support, dmaengine APIs need to >>>>>> terminate in non-atomic context before unmapping the dma buffers. >>>>>> >>>>>> To facilitate this, remove the finish_tasklet and move the call of >>>>>> sdhci_request_done() to the threaded_irq() callback. >>>>> >>>>> The irq thread has a higher latency than the tasklet. The performance drop >>>>> is measurable on the system I tried: >>>>> >>>>> Before: >>>>> >>>>> # dd if=/dev/mmcblk1 of=/dev/null bs=1G count=1 & >>>>> 1+0 records in >>>>> 1+0 records out >>>>> 1073741824 bytes (1.1 GB) copied, 4.44502 s, 242 MB/s >>>>> >>>>> After: >>>>> >>>>> # dd if=/dev/mmcblk1 of=/dev/null bs=1G count=1 & >>>>> 1+0 records in >>>>> 1+0 records out >>>>> 1073741824 bytes (1.1 GB) copied, 4.50898 s, 238 MB/s >>>>> >>>>> So we only want to resort to the thread for the error case. >>>>> >>>> >>>> Sorry for the late response here, but this is about 1.6% decrease. I >>>> tried out the same commands on a dra7xx board here (with about 5 >>>> consecutive dd of 1GB) and the average decrease was 0.3%. I believe you >>>> will also find a lesser percentage change if you average over multiple >>>> dd commands. >>>> >>>> Is this really so significant that we have to maintain two different >>>> bottom halves and keep having difficulty with adding APIs that can sleep? >>> >>> It is a performance drop that can be avoided, so it might as well be. >>> Splitting the success path from the failure path is common for I/O drivers >>> for similar reasons as here: the success path can be optimized whereas the >>> failure path potentially needs to sleep. >> >> Understood. You wanna keep the success path as fast as possible. > > Sry, I've not completely followed this series, but I'd like to add 5c > > It's good thing to get rid of tasklets hence RT Linux kernel is actively moving towards to LKML > and there everything handled in threads (even networking trying to get rid of softirqs). > > Performance is pretty relative thing here - just try to run network traffic in parallel, and > there are no control over it comparing to threads. Now way to assign priority or pin to CPU. There is a 2007 LWN article(https://lwn.net/Articles/239633/) which talks about removing tasklets altogether. I wonder what happened after that. Thanks, Faiz