From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752381AbeDLBaz (ORCPT ); Wed, 11 Apr 2018 21:30:55 -0400 Received: from mail-pf0-f193.google.com ([209.85.192.193]:37662 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751841AbeDLBax (ORCPT ); Wed, 11 Apr 2018 21:30:53 -0400 X-Google-Smtp-Source: AIpwx4/wGgVPYr78q4V8gnqyBb9OWsM5GqQXi2e6l4NrcOtjo2MS+YVKxZlC0Mewe+P7NvGH6i/d/Q== Subject: Re: [PATCH v2] dec: tulip: de4x5: Replace mdelay with usleep_range in de4x5_hw_init To: James Bottomley , davem@davemloft.net, stephen@networkplumber.org, johannes.berg@intel.com, arvind.yadav.cs@gmail.com, dhowells@redhat.com Cc: netdev@vger.kernel.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org References: <1523461182-5897-1-git-send-email-baijiaju1990@gmail.com> <1523463379.3221.18.camel@HansenPartnership.com> From: Jia-Ju Bai Message-ID: <8bac3385-97c6-fff1-17c6-11f5e98a039a@gmail.com> Date: Thu, 12 Apr 2018 09:30:32 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <1523463379.3221.18.camel@HansenPartnership.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/4/12 0:16, James Bottomley wrote: > On Wed, 2018-04-11 at 23:39 +0800, Jia-Ju Bai wrote: >> de4x5_hw_init() is never called in atomic context. >> >> de4x5_hw_init() is only called by de4x5_pci_probe(), which is only >> set as ".probe" in struct pci_driver. >> >> Despite never getting called from atomic context, de4x5_hw_init() >> calls mdelay() to busily wait. This is not necessary and can be >> replaced with usleep_range() to avoid busy waiting. >> >> This is found by a static analysis tool named DCNS written by myself. >> And I also manually check it. > Did you actually test this? The usual reason for wanting m/udelay is > that the timing must be exact. The driver is filled with mdelay()s for > this reason. The one you've picked on is in the init path so it won't > affect the runtime in any way. I also don't think we have the hrtimer > machinery for usleep_range() to work properly on parisc, so I don't > think the replacement works. > > James > Hello, James. Thanks for your reply :) I agree that usleep_range() here will not much affect the real execution of this driver. But I think usleep_range() can more opportunity for other threads to use the CPU core to schedule during waiting. That is why I detect mdelay() that can be replaced with msleep() or usleep_range(). Best wishes, Jia-Ju Bai