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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 C072CC10F14 for ; Tue, 15 Oct 2019 08:00:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F43C217F9 for ; Tue, 15 Oct 2019 08:00:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571126441; bh=vcYq/iS4MSEtutlQdlZl0mkXyEpA5264rRCfQEISiUA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=KllUxoskEt4l83J6NVKkOQMcTVtXHTLrEZD5F0ps2bQsO+FN+/cMBRhkMgu3vw8du o+MOEUzDJ7Ul1XZjD39IVE4o9rE4aiIyNKIrylHmV7+OsHALNxZ/7Vi5mVxENYzWvN 1tYYM5zMi+U+7Z3iiUhHl5xVRzV0iMTtpV/CUiNc= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727454AbfJOIAl (ORCPT ); Tue, 15 Oct 2019 04:00:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:42300 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727295AbfJOIAl (ORCPT ); Tue, 15 Oct 2019 04:00:41 -0400 Received: from localhost (unknown [193.47.165.251]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F1E292089C; Tue, 15 Oct 2019 08:00:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1571126439; bh=vcYq/iS4MSEtutlQdlZl0mkXyEpA5264rRCfQEISiUA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uVmgibbDj5aduRK/kdHGC93LNLIMEHNVpXIdyIEaa8NfvB39C5mF9t0V+UwHtonrt RBb4zljAqzt5n0LUcw4ZO52X9GyfJ8mOQMFCrwCAQAo3vynnFbKs9XURLY/79pvxOA Q47K4igcYSvJsyzc9buNt5GJd12sofnG0TdDmWK0= Date: Tue, 15 Oct 2019 11:00:36 +0300 From: Leon Romanovsky To: "Liuyixian (Eason)" Cc: linux-rdma@vger.kernel.org, jgg@ziepe.ca, dledford@redhat.com, linuxarm@huawei.com Subject: Re: [PATCH for-next] RDMA/hns: Bugfix for flush cqe in case softirq and multi-process Message-ID: <20191015080036.GC6957@unreal> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.12.1 (2019-06-15) Sender: linux-rdma-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org 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. > > Thanks. >