From mboxrd@z Thu Jan 1 00:00:00 1970 From: arvindY Subject: Re: [PATCH v2] dec: tulip: de4x5: Replace mdelay with usleep_range in de4x5_hw_init Date: Thu, 12 Apr 2018 07:51:42 +0530 Message-ID: <5ACEC2B6.9080904@gmail.com> References: <1523461182-5897-1-git-send-email-baijiaju1990@gmail.com> <1523463379.3221.18.camel@HansenPartnership.com> <8bac3385-97c6-fff1-17c6-11f5e98a039a@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, linux-parisc@vger.kernel.org, linux-kernel@vger.kernel.org To: Jia-Ju Bai , James Bottomley , davem@davemloft.net, stephen@networkplumber.org, johannes.berg@intel.com, dhowells@redhat.com Return-path: In-Reply-To: <8bac3385-97c6-fff1-17c6-11f5e98a039a@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thursday 12 April 2018 07:00 AM, Jia-Ju Bai wrote: > > > 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(). > James is right, You have added all usleep_range() during system boot-up time. During boot-up system will run as single threaded. Where this change will not make much sense. System first priority is match the exact timing on each and every boot-up. ~arvind > > Best wishes, > Jia-Ju Bai