Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757054AbaFSByA (ORCPT ); Wed, 18 Jun 2014 21:54:00 -0400 Received: from rtits2.realtek.com ([60.250.210.242]:46137 "EHLO rtits2.realtek.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756958AbaFSBx6 (ORCPT ); Wed, 18 Jun 2014 21:53:58 -0400 X-SpamFilter-By: BOX Solutions SpamTrap 5.39 with qID s5J1qLMg005860, This message is accepted by code: ctloc85258 Message-ID: <53A24379.2060502@realsil.com.cn> Date: Thu, 19 Jun 2014 09:57:13 +0800 From: micky User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: Ulf Hansson CC: Samuel Ortiz , Lee Jones , Chris Ball , , "linux-kernel@vger.kernel.org" , linux-mmc , Greg Kroah-Hartman , Dan Carpenter , Roger , "Wei WANG" Subject: Re: [PATCH 2/2] mmc: rtsx: add support for async request References: <7b58fb0b0915ea0b0838404c74ec22a3b6e5f5a8.1402037565.git.micky_ching@realsil.com.cn> <539EB43B.8070707@realsil.com.cn> <539F9412.3010209@realsil.com.cn> <53A0E89F.9010006@realsil.com.cn> <53A16517.7050705@realsil.com.cn> In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [172.29.41.103] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/18/2014 07:03 PM, Ulf Hansson wrote: > On 18 June 2014 12:08, micky wrote: >> On 06/18/2014 03:39 PM, Ulf Hansson wrote: >>> On 18 June 2014 03:17, micky wrote: >>>> On 06/17/2014 03:45 PM, Ulf Hansson wrote: >>>>> On 17 June 2014 03:04, micky wrote: >>>>>> On 06/16/2014 08:40 PM, Ulf Hansson wrote: >>>>>>> On 16 June 2014 11:09, micky wrote: >>>>>>>> On 06/16/2014 04:42 PM, Ulf Hansson wrote: >>>>>>>>>> @@ -36,7 +37,10 @@ struct realtek_pci_sdmmc { >>>>>>>>>>> struct rtsx_pcr *pcr; >>>>>>>>>>> struct mmc_host *mmc; >>>>>>>>>>> struct mmc_request *mrq; >>>>>>>>>>> + struct workqueue_struct *workq; >>>>>>>>>>> +#define SDMMC_WORKQ_NAME "rtsx_pci_sdmmc_workq" >>>>>>>>>>> >>>>>>>>>>> + struct work_struct work; >>>>>>>>> I am trying to understand why you need a work/workqueue to implement >>>>>>>>> this feature. Is that really the case? >>>>>>>>> >>>>>>>>> Could you elaborate on the reasons? >>>>>>>> Hi Uffe, >>>>>>>> >>>>>>>> we need return as fast as possible in mmc_host_ops >>>>>>>> request(ops->request) >>>>>>>> callback, >>>>>>>> so the mmc core can continue handle next request. >>>>>>>> when next request everything is ready, it will wait previous done(if >>>>>>>> not >>>>>>>> done), >>>>>>>> then call ops->request(). >>>>>>>> >>>>>>>> we can't use atomic context, because we use mutex_lock() to protect >>>>>>> ops->request should never executed in atomic context. Is that your >>>>>>> concern? >>>>>> Yes. >>>>> Okay. Unless I missed your point, I don't think you need the >>>>> work/workqueue. >>>> any other method? >>>> >>>>> Because, ops->request isn't ever executed in atomic context. That's >>>>> due to the mmc core, which handles the async mechanism, are waiting >>>>> for a completion variable in process context, before it invokes the >>>>> ops->request() callback. >>>>> >>>>> That completion variable will be kicked, from your host driver, when >>>>> you invoke mmc_request_done(), . >>>> Sorry, I don't understand here, how kicked? >>> mmc_request_done() >>> ->mrq->done() >>> ->mmc_wait_done() >>> ->complete(&mrq->completion); >>> >>>> I think the flow is: >>>> - not wait for first req >>>> - init mrq->done >>>> - ops->request() --- A.rtsx: start queue >>>> work. >>>> - continue fetch next req >>>> - prepare next req ok, >>>> - wait previous done. --- B.(mmc_request_done() may be >>>> called >>>> at any time from A to B) >>>> - init mrq->done >>>> - ops->request() --- C.rtsx: start queue >>>> next work. >>>> ... >>>> and seems no problem. >>> Right, I don't think there are any _problem_ by using the workqueue as >>> you have implemented, but I am questioning if it's correct. Simply >>> because I don't think there are any reasons to why you need a >>> workqueue, it doesn't solve any problem for you - it just adds >>> overhead. >> Hi Uffe, >> >> we have two driver under mfd, the rtsx-mmc and rtsx-ms, >> we use mutex lock(pcr_mutex) to protect resource, >> when we handle mmc request, we need hold the mutex until we finish the >> request, >> so it will not interruptted by rtsx-ms request. > Ahh, I see. Now, _that_ explains why you want the workqueue. :-) Thanks! > >> If we not use workq, once the request hold the mutex, we have to wait until >> the request finish, >> then release mutex, so the mmc core is blocking at here. >> To implement nonblocking request, we have to use workq. > One minor suggestion below, please consider this as an optimization > which goes outside the context of this patch. > > There are cases when I think you should be able to skip the overhead > from scheduling the work from ->request(). Those cases can be > described as when the mutex are available which can be tested by using > mutex_trylock(). Thanks for your suggestion. we need schedule the work every time mmc core call ops->request(), if we want to handle request, we need hold mutex and do the work. so mutex_trylock() will not help decrease overhead. if we not schedule the work, the ops->request will do nothing. Best Regards. micky > Kind regards > Uffe > . > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/