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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 E1A48C433E9 for ; Fri, 5 Mar 2021 08:13:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B9B3364E45 for ; Fri, 5 Mar 2021 08:13:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229576AbhCEINE (ORCPT ); Fri, 5 Mar 2021 03:13:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229464AbhCEIMt (ORCPT ); Fri, 5 Mar 2021 03:12:49 -0500 Received: from mail-ej1-x631.google.com (mail-ej1-x631.google.com [IPv6:2a00:1450:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B5A24C061574 for ; Fri, 5 Mar 2021 00:12:48 -0800 (PST) Received: by mail-ej1-x631.google.com with SMTP id bm21so1725973ejb.4 for ; Fri, 05 Mar 2021 00:12:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc:content-transfer-encoding; bh=MBq2dGqsKbpMQki8GbETIioPY9a6dWwdNAOqi//tVmc=; b=porWskft+5t/TBuUshloZFxNjeupZlZ23+ErLyvvzGuXRkkEYh0vvQbJbucntZdqAg 0ES+45LLefK3HEONaNlvegQ1vO5iTeel907vOXTK3EePZ8izS8gwXWV5fyWAY4GWOZ0Z 5tk/5HS7ka14qwrbaJgTdKn790HLoPQHjao2dSkPjEvBMV4vj5LRycnQyCZoxw043iYM jX88gNjUJRTSNabDKBY1BHfqKcuzf8tJL18lOYbJUWwBIb2czXRDBoUeZKrlNpqB+vo4 EedABKKbBL3IqVnaB4xIsYUGuZbmMZwsEbqSBko3xGQ6k4GCN0iLRX/ROIY/R//Lo0Zc MnaA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc:content-transfer-encoding; bh=MBq2dGqsKbpMQki8GbETIioPY9a6dWwdNAOqi//tVmc=; b=RwetiQ3VzEMVHF3EzikluZjc8wYGbsoEt1ZwhseUWQhAU24asUSRvQQ3EzSA7WaHBu Kw+rhcO1Gn3zU8jD5sp7DPzde82XQi5BeNPEZMWX8VOTuzq8D90QG3Ef3VUdnS7qvGox WFID/TjEy4Jxysa5gmipCDlpGWI1n+a7qYC/bxwDCZzWQnNX0qAyocfd8c90kCCouDcC zFoxyGBeEi9gCyJ6epJRM8ra3w0vV13x5HW7m6PE/J3cwcLNU0zhOsOasR2kTksbKH+M 1Rr7RxvEc1JZ9CUr/OvYiXf7WCCSVUb/G+L9Zzs5U18i7k68Y36uwwtxcTu1eSoswULf lVtg== X-Gm-Message-State: AOAM531AjhjS6pwQtDpUEKnMSS/1OsNCQshsojbRLeHJb4FkWjfQzviY 582Y4pO7Krc4ReJ79Fzh4N49mL8zpsmG5uaps/Wh X-Google-Smtp-Source: ABdhPJwBVpzIGvikUm/YZyRyq/dpIgXIV3a8HsfaiFFYOPN+MrInYoK8nhTRYFkzCPSxGa96na2IDVTi9Bc9HIxIN8s= X-Received: by 2002:a17:906:7b8d:: with SMTP id s13mr1273371ejo.247.1614931967461; Fri, 05 Mar 2021 00:12:47 -0800 (PST) MIME-Version: 1.0 References: <20210223115048.435-1-xieyongji@bytedance.com> <20210223115048.435-11-xieyongji@bytedance.com> <2d3418d9-856c-37ee-7614-af5b721becd7@redhat.com> In-Reply-To: From: Yongji Xie Date: Fri, 5 Mar 2021 16:12:36 +0800 Message-ID: Subject: Re: Re: [RFC v4 10/11] vduse: Introduce a workqueue for irq injection To: Jason Wang Cc: "Michael S. Tsirkin" , Stefan Hajnoczi , Stefano Garzarella , Parav Pandit , Bob Liu , Christoph Hellwig , Randy Dunlap , Matthew Wilcox , viro@zeniv.linux.org.uk, Jens Axboe , bcrl@kvack.org, Jonathan Corbet , virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, kvm@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Mar 5, 2021 at 3:37 PM Jason Wang wrote: > > > On 2021/3/5 3:27 =E4=B8=8B=E5=8D=88, Yongji Xie wrote: > > On Fri, Mar 5, 2021 at 3:01 PM Jason Wang wrote: > >> > >> On 2021/3/5 2:36 =E4=B8=8B=E5=8D=88, Yongji Xie wrote: > >>> On Fri, Mar 5, 2021 at 11:42 AM Jason Wang wrot= e: > >>>> On 2021/3/5 11:30 =E4=B8=8A=E5=8D=88, Yongji Xie wrote: > >>>>> On Fri, Mar 5, 2021 at 11:05 AM Jason Wang wr= ote: > >>>>>> On 2021/3/4 4:58 =E4=B8=8B=E5=8D=88, Yongji Xie wrote: > >>>>>>> On Thu, Mar 4, 2021 at 2:59 PM Jason Wang w= rote: > >>>>>>>> On 2021/2/23 7:50 =E4=B8=8B=E5=8D=88, Xie Yongji wrote: > >>>>>>>>> This patch introduces a workqueue to support injecting > >>>>>>>>> virtqueue's interrupt asynchronously. This is mainly > >>>>>>>>> for performance considerations which makes sure the push() > >>>>>>>>> and pop() for used vring can be asynchronous. > >>>>>>>> Do you have pref numbers for this patch? > >>>>>>>> > >>>>>>> No, I can do some tests for it if needed. > >>>>>>> > >>>>>>> Another problem is the VIRTIO_RING_F_EVENT_IDX feature will be us= eless > >>>>>>> if we call irq callback in ioctl context. Something like: > >>>>>>> > >>>>>>> virtqueue_push(); > >>>>>>> virtio_notify(); > >>>>>>> ioctl() > >>>>>>> ------------------------------------------------- > >>>>>>> irq_cb() > >>>>>>> virtqueue_get_buf() > >>>>>>> > >>>>>>> The used vring is always empty each time we call virtqueue_push()= in > >>>>>>> userspace. Not sure if it is what we expected. > >>>>>> I'm not sure I get the issue. > >>>>>> > >>>>>> THe used ring should be filled by virtqueue_push() which is done b= y > >>>>>> userspace before? > >>>>>> > >>>>> After userspace call virtqueue_push(), it always call virtio_notify= () > >>>>> immediately. In traditional VM (vhost-vdpa) cases, virtio_notify() > >>>>> will inject an irq to VM and return, then vcpu thread will call > >>>>> interrupt handler. But in container (virtio-vdpa) cases, > >>>>> virtio_notify() will call interrupt handler directly. So it looks l= ike > >>>>> we have to optimize the virtio-vdpa cases. But one problem is we do= n't > >>>>> know whether we are in the VM user case or container user case. > >>>> Yes, but I still don't get why used ring is empty after the ioctl()? > >>>> Used ring does not use bounce page so it should be visible to the ke= rnel > >>>> driver. What did I miss :) ? > >>>> > >>> Sorry, I'm not saying the kernel can't see the correct used vring. I > >>> mean the kernel will consume the used vring in the ioctl context > >>> directly in the virtio-vdpa case. In userspace's view, that means > >>> virtqueue_push() is used vring's producer and virtio_notify() is used > >>> vring's consumer. They will be called one by one in one thread rather > >>> than different threads, which looks odd and has a bad effect on > >>> performance. > >> > >> Yes, that's why we need a workqueue (WQ_UNBOUND you used). Or do you > >> want to squash this patch into patch 8? > >> > >> So I think we can see obvious difference when virtio-vdpa is used. > >> > > But it looks like we don't need this workqueue in vhost-vdpa cases. > > Any suggestions? > > > I haven't had a deep thought. But I feel we can solve this by using the > irq bypass manager (or something similar). Then we don't need it to be > relayed via workqueue and vdpa. But I'm not sure how hard it will be. > Or let vdpa bus drivers give us some information? > Do you see any obvious performance regression by using the workqueue? Or > we can optimize it in the future. > Agree. Thanks, Yongji