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 42BA4C433E6 for ; Fri, 5 Mar 2021 06:37:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F162765018 for ; Fri, 5 Mar 2021 06:37:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229558AbhCEGhF (ORCPT ); Fri, 5 Mar 2021 01:37:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45932 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229582AbhCEGhF (ORCPT ); Fri, 5 Mar 2021 01:37:05 -0500 Received: from mail-ed1-x536.google.com (mail-ed1-x536.google.com [IPv6:2a00:1450:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8AF8FC061756 for ; Thu, 4 Mar 2021 22:37:04 -0800 (PST) Received: by mail-ed1-x536.google.com with SMTP id w9so1022120edt.13 for ; Thu, 04 Mar 2021 22:37:04 -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=ye59LOuGJNa6hn8POa8Q5ZSuRRH1Gakg9Xz+Jk2Jink=; b=vu5x9yYj2w7fljnGMRc6sBWOUbFHyR11j69ZlJAT7KX2UQczG6/XSMQaQI1RX2tFPv 2kkU3lHS+iIDkfOCg4mQyMdvK7y6fMgg2xx0/SkmzfQUN6tSpIQ1xXSgyWQ/ND+xwiD4 MVXuAU9FlzuArjViWE/Hv4l9ChOYOX7qVlD2Hc0SE9jhRGCPALFaDdB1YYRooTHECR0x Pfg9lskpz9RqMJooT6/AurbUMhQX23872AJPDRDmvHE1Z53wEw9H9+eJNCXfM6dJ6Bz4 yt6hFmIrDfgXZYB8bf7qzXBmDXZLdu9AHXjgEs9xOTmWkhJH9HMIva/mOMFj0BOhvzo4 VXkQ== 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=ye59LOuGJNa6hn8POa8Q5ZSuRRH1Gakg9Xz+Jk2Jink=; b=SjqSoN739xM8Cc8eFAD5mxHxKZL8Fn4y2sVJ7eTy6lRBqDLNphllMU3483f8zy1uTY 9d2IXdxwTtZDRc5Y8O/mk9cph2PvksiitUV8RbwKJ2f7d6KPYaFz4z3u/tv/rFFPdTjt 4DHKbCAk+CCUlnhdwoPcxN70Ex9f+sYDRMKQQq0JvE4oCyzaFGo1xT7hocbtdmBiy620 rtln8/oDOj+zw8AP2qSQtXzvJI7RQaqKloI4UkvRedJM+Gdv0a4DoqXW//FSNTR4L6d6 y2JFvaI9hOt4p5zfwCNoXzvXJWfZAqcZ9pCwYrscY9YvFQPpySYjRK/MpU3/aiY8fTUk xKcA== X-Gm-Message-State: AOAM532hXke2rP6YLLbszitceMDCC1qREQa61MLZWNCYg+ko6Ira1Nkk 0Lqwj6BrZ9+3D64yTMQ4INOUT0RwdESOtDp2s0r2 X-Google-Smtp-Source: ABdhPJyzGm5l6y0XncFMOdG/BrxDoWZXw1mC+/B9mBP/5bP1IX8avxfXqpHQX94dMqW8zB6Sk/QjqAEUmZOZe1o8d2g= X-Received: by 2002:a05:6402:3122:: with SMTP id dd2mr7725434edb.253.1614926223212; Thu, 04 Mar 2021 22:37:03 -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 14:36:51 +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 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 wrote: > >> > >> 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 wrote= : > >>>> 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 useles= s > >>> 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 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 like > > 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 kernel > 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. Thanks, Yongji