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 E1A83C433E9 for ; Fri, 5 Mar 2021 07:27:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9430165022 for ; Fri, 5 Mar 2021 07:27:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229523AbhCEH10 (ORCPT ); Fri, 5 Mar 2021 02:27:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56698 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229494AbhCEH10 (ORCPT ); Fri, 5 Mar 2021 02:27:26 -0500 Received: from mail-ed1-x529.google.com (mail-ed1-x529.google.com [IPv6:2a00:1450:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BEEA8C06175F for ; Thu, 4 Mar 2021 23:27:25 -0800 (PST) Received: by mail-ed1-x529.google.com with SMTP id h10so1199474edl.6 for ; Thu, 04 Mar 2021 23:27:25 -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=hM0XVBnBjvo6Mcn0O7eJCM7OuQBmW0OA0z+7Q1PSpD0=; b=dNI/7ddrUUBV1gT2sOck2Qs9XORP9rv7TZSeSwpRwn1+PFmreDEPtnkLFrU+Jivwv8 y6BxcPLp3QycfOG0HL/1ux+3esOM0tZiTu4Ja2dB6gjQBefRQX/VOvmGDcsS1En+RktH bKQXxeLBiyMINDjZRY7dKDlghINiR7QrhlSL3DZaEU/M2MCJQnnQ/Rtf/WYqP2Cg+AhQ AwTDcV08MI0milFSazXs7mjCrTK80d8vB5F3FqP812oU+kVxVgaMAkE7B3WgHkFCU0mS whFfjNTBtBiWqLpZO4leil6ySnNP8sk/yTumXztNWjcCj/83mtMRavXjLZXQ16MzZYFd mq6Q== 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=hM0XVBnBjvo6Mcn0O7eJCM7OuQBmW0OA0z+7Q1PSpD0=; b=VAtCdYRbRD6HT6q6Ij6QNKYoS6is++yIGz7IDC3UjH83AHpdHLp/Dm8I0H61abwHXq zatK+iqTSrbC48jnpQxj6F5lsnaTRuebVOFv57Gr3IwBbQnTiFwSCmtYwh+XdA10OoM7 oCtq3npTPk7Enfkq92qLDs2XxTFOkYPhXPBjM7pUr3rezv42VR1T5uqzdPiU/8qWeBDp N1+33ycJQPFfeLFFV3SE2vhxqyFTurxJsBCIf8aP1s8WYciU4FRPYEgwHBXb2VbhNy53 a/RMuMRH4zauX0yAtgVw+JRxvXOe+veiwg33ZaqHxrB38ExHyXp37l6yVY9PEbXYpcyS AwRA== X-Gm-Message-State: AOAM5325DD+5nCQqFqOf7jYe4iCS6Y4w/sqidWrdFFPHNYwhy0Heaa5C h/pix9Phr0BwojnMTWeWSaZuUj1Msvvqf6UoKva0R8t3aQ== X-Google-Smtp-Source: ABdhPJxue5Ac0KWm5LuWB3zHp3MbVN6tHMJsqST8murh5iUTYzZb9u6sReCwvdokxCB2Xhd8hKmcmRqFLWouZ7AI6V4= X-Received: by 2002:aa7:d687:: with SMTP id d7mr7858393edr.118.1614929244463; Thu, 04 Mar 2021 23:27:24 -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 15:27:13 +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 3:01 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 wrote: > >> > >> 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 wrot= e: > >>>> 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 wro= te: > >>>>>> 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 usel= ess > >>>>> 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() i= n > >>>>> 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 by > >>>> 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 lik= e > >>> we have to optimize the virtio-vdpa cases. But one problem is we don'= 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 kern= el > >> 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? Thanks, Yongji