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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 CC866C4332B for ; Mon, 11 Jan 2021 19:23:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B23BA22CAE for ; Mon, 11 Jan 2021 19:23:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404107AbhAKTXd (ORCPT ); Mon, 11 Jan 2021 14:23:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:33836 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404152AbhAKTX3 (ORCPT ); Mon, 11 Jan 2021 14:23:29 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E6432AB7F; Mon, 11 Jan 2021 19:22:47 +0000 (UTC) Date: Mon, 11 Jan 2021 11:22:40 -0800 From: Davidlohr Bueso To: Hillf Danton Cc: jacmet@sunsite.dk, gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Davidlohr Bueso Subject: Re: [PATCH] usb/c67x00: Replace tasklet with work Message-ID: <20210111192240.osls6hi5wmnw76ts@offworld> References: <20210111044050.86763-1-dave@stgolabs.net> <20210111090533.1450-1-hdanton@sina.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20210111090533.1450-1-hdanton@sina.com> User-Agent: NeoMutt/20201120 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 11 Jan 2021, Hillf Danton wrote: >On Sun, 10 Jan 2021 20:40:50 -0800 Davidlohr Bueso wrote: >> Tasklets have long been deprecated as being too heavy on the system >> by running in irq context - and this is not a performance critical >> path. If a higher priority process wants to run, it must wait for >> the tasklet to finish before doing so. >> >> c67x00_do_work() will now run in process context and have further >> concurrency (tasklets being serialized among themselves), but this >> is done holding the c67x00->lock, so it should be fine. Furthermore, >> this patch fixes the usage of the lock in the callback as otherwise >> it would need to be irq-safe. > >Can you add a couple of words about the need to be irq-safe because >no lock is taken for scheduling either tasklet or work? I was refering to the locking in the c67x00_do_work() tasklet callback. Because it is currently under irq it should be disabling irq (or at least BH) but after this patch that is no longer the case. >> >> Signed-off-by: Davidlohr Bueso >> --- >> drivers/usb/c67x00/c67x00-hcd.h | 2 +- >> drivers/usb/c67x00/c67x00-sched.c | 12 +++++++----- >> 2 files changed, 8 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/usb/c67x00/c67x00-hcd.h b/drivers/usb/c67x00/c67x00-hcd.h >> index 6b6b04a3fe0f..6332a6b5dce6 100644 >> --- a/drivers/usb/c67x00/c67x00-hcd.h >> +++ b/drivers/usb/c67x00/c67x00-hcd.h >> @@ -76,7 +76,7 @@ struct c67x00_hcd { >> u16 next_td_addr; >> u16 next_buf_addr; >> >> - struct tasklet_struct tasklet; >> + struct work_struct work; >> >> struct completion endpoint_disable; >> >> diff --git a/drivers/usb/c67x00/c67x00-sched.c b/drivers/usb/c67x00/c67x00-sched.c >> index e65f1a0ae80b..af60f4fdd340 100644 >> --- a/drivers/usb/c67x00/c67x00-sched.c >> +++ b/drivers/usb/c67x00/c67x00-sched.c >> @@ -1123,24 +1123,26 @@ static void c67x00_do_work(struct c67x00_hcd *c67x00) >> >> /* -------------------------------------------------------------------------- */ >> >> -static void c67x00_sched_tasklet(struct tasklet_struct *t) >> +static void c67x00_sched_work(struct work_struct *work) >> { >> - struct c67x00_hcd *c67x00 = from_tasklet(c67x00, t, tasklet); >> + struct c67x00_hcd *c67x00; >> + >> + c67x00 = container_of(work, struct c67x00_hcd, work); >> c67x00_do_work(c67x00); >> } >> >> void c67x00_sched_kick(struct c67x00_hcd *c67x00) >> { >> - tasklet_hi_schedule(&c67x00->tasklet); >> + queue_work(system_highpri_wq, &c67x00->work); > >Better if one line comment is added for highpri, given this is not a >performance critical path. I'm not sure the value here, considering the highprio is not being changed here. There are a few drivers who use highpri workqueue and care about latencies but they are still not performance critical (to the overall system that is, which is what I meant by that). Thanks, Davidlohr