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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 6EB84CA9EA0 for ; Mon, 28 Oct 2019 09:35:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 48EEB214E0 for ; Mon, 28 Oct 2019 09:35:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732722AbfJ1Jfe (ORCPT ); Mon, 28 Oct 2019 05:35:34 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:4775 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1732678AbfJ1Jfe (ORCPT ); Mon, 28 Oct 2019 05:35:34 -0400 Received: from DGGEMS407-HUB.china.huawei.com (unknown [172.30.72.59]) by Forcepoint Email with ESMTP id 327805965A346FF4C17F; Mon, 28 Oct 2019 17:35:31 +0800 (CST) Received: from [127.0.0.1] (10.74.223.196) by DGGEMS407-HUB.china.huawei.com (10.3.19.207) with Microsoft SMTP Server id 14.3.439.0; Mon, 28 Oct 2019 17:35:23 +0800 Subject: Re: [PATCH for-next] RDMA/hns: Bugfix for flush cqe in case softirq and multi-process To: Leon Romanovsky CC: , , , References: <1567686671-4331-1-git-send-email-liweihang@hisilicon.com> <20190908080303.GC26697@unreal> <20190910075216.GX6601@unreal> <94ad1f56-afc6-ec78-4aa2-85d03c644031@huawei.com> <0d4ce391-6619-783d-55a8-fa2524af7b9c@huawei.com> <20190923050125.GK14368@unreal> <1224a3a0-50fb-dd6a-f22e-833e74ec77c3@huawei.com> <20191015080036.GC6957@unreal> From: "Liuyixian (Eason)" Message-ID: Date: Mon, 28 Oct 2019 17:34:21 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.1.1 MIME-Version: 1.0 In-Reply-To: <20191015080036.GC6957@unreal> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.74.223.196] X-CFilter-Loop: Reflected Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 2019/10/15 16:00, Leon Romanovsky wrote: > On Sat, Oct 12, 2019 at 11:53:36AM +0800, Liuyixian (Eason) wrote: >> >> >> On 2019/9/24 11:54, Liuyixian (Eason) wrote: >>> >>> >>> On 2019/9/23 13:01, Leon Romanovsky wrote: >>>> On Fri, Sep 20, 2019 at 11:55:56AM +0800, Liuyixian (Eason) wrote: >>>>> >>>>> >>>>> On 2019/9/11 21:17, Liuyixian (Eason) wrote: >>>>>> >>>>>> >>>>>> On 2019/9/10 15:52, Leon Romanovsky wrote: >>>>>>> On Tue, Sep 10, 2019 at 02:40:20PM +0800, Liuyixian (Eason) wrote: >>>>>>>> >>>>>>>> >>>>>>>> On 2019/9/8 16:03, Leon Romanovsky wrote: >>>>>>>>> On Thu, Sep 05, 2019 at 08:31:11PM +0800, Weihang Li wrote: >>>>>>>>>> From: Yixian Liu >>>>>>>>>> >>>>>>>>>> Hip08 has the feature flush cqe, which help to flush wqe in workqueue >>>>>>>>>> (sq and rq) when error happened by transmitting producer index with >>>>>>>>>> mailbox to hardware. Flush cqe is emplemented in post send and recv >>>>>>>>>> verbs. However, under NVMe cases, these verbs will be called under >>>>>>>>>> softirq context, and it will lead to following calltrace with >>>>>>>>>> current driver as mailbox used by flush cqe can go to sleep. >>>>>>>>>> >>>>>>>>>> This patch solves this problem by using workqueue to do flush cqe, >>>>>>>>> >>>>>>>>> Unbelievable, almost every bug in this driver is solved by introducing >>>>>>>>> workqueue. You should fix "sleep in flush path" issue and not by adding >>>>>>>>> new workqueue. >>>>>>>>> >>>>>>>> Hi Leon, >>>>>>>> >>>>>>>> Thanks for the comment. >>>>>>>> Up to now, for hip08, only one place use workqueue in hns_roce_hw_v2.c >>>>>>>> where for irq prints. >>>>>>> >>>>>>> Thanks to our lack of desire to add more workqueues and previous patches >>>>>>> which removed extra workqueues from the driver. >>>>>>> >>>>>> Thanks, I see. >>>>>> >>>>>>>> >>>>>>>> The solution for flush cqe in this patch is as follow: >>>>>>>> While flush cqe should be implement, the driver should modify qp to error state >>>>>>>> through mailbox with the newest product index of sq and rq, the hardware then >>>>>>>> can flush all outstanding wqes in sq and rq. >>>>>>>> >>>>>>>> That's the whole mechanism of flush cqe, also is the flush path. We can't >>>>>>>> change neither mailbox sleep attribute or flush cqe occurred in post send/recv. >>>>>>>> To avoid the calltrace of flush cqe in post verbs under NVMe softirq, >>>>>>>> use workqueue for flush cqe seems reasonable. >>>>>>>> >>>>>>>> As far as I know, there is no other alternative solution for this situation. >>>>>>>> I will be very grateful if you reminder me more information. >>>>>>> >>>>>>> ib_drain_rq/ib_drain_sq/ib_drain_qp???? >>>>>>> >>>>>> Hi Leon, >>>>>> >>>>>> I think these interfaces are designed for application to check that all wqes >>>>>> have been processed by hardware, so called drain or flush. However, it is not >>>>>> the same as the flush in this patch. The solution in this patch is used >>>>>> to help the hardware generate flush cqes for outstanding wqes while qp error. >>>>>> >>>>> Hi Leon, >>>>> >>>>> What's your opinion about above? Do you have any further comments? >>>> >>>> My opinion didn't change, you need to read discussions about ib_drain_*() >>>> functions, how and why they were introduced. It is a way to go. >>>> >>>> Thanks >>> >>> Hi Leon, >>> >>> Thanks a lot! I will dig those functions for my problem. >>> >> >> Hi Leon, >> >> I have analysis the mechanism of ib_drain_(qp, sq, rq), that's okay to use >> it instead of our flush cqe as both of them are calling modify qp to error >> state in flush path. >> >> However, both ib_drain_* and flush cqe will face the same problem as declared >> in previous emails, that is, in NVME case, post verbs will be called under >> **softirq**, which will result to calltrace as mailbox used in modify qp >> (flush path) can sleep, this is not allowed under softirq. >> >> Thus, to resolve above calltrace (sleep in softirq), using workqueue as in >> this patch seems is a reasonable solution regardless of ib_drain_qp or >> flush cqe is called in the workqueue. >> >> I think it is not a good idea to fix sleep in flush path (actually referred >> to mailbox used in modify qp) as the mailbox is such a mature mechanism. > > No, it is not reasonable solution. > Hi Leon, I have explained this issue better in another patch set and pruned other logic. Thanks a lot for your review! Best regards. Eason >> >> Thanks. >> > > . >