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 399E9C433E6 for ; Mon, 8 Mar 2021 04:50:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0CF5265166 for ; Mon, 8 Mar 2021 04:50:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232548AbhCHEuW (ORCPT ); Sun, 7 Mar 2021 23:50:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45074 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232565AbhCHEuT (ORCPT ); Sun, 7 Mar 2021 23:50:19 -0500 Received: from mail-ed1-x52b.google.com (mail-ed1-x52b.google.com [IPv6:2a00:1450:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9348DC06174A for ; Sun, 7 Mar 2021 20:50:19 -0800 (PST) Received: by mail-ed1-x52b.google.com with SMTP id bd6so12667452edb.10 for ; Sun, 07 Mar 2021 20:50:19 -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=f8lrR0ZiQSWaL4KkWmwSgVmShpah+Hqkiq/7u9MC3Ec=; b=bmd/qNoUyZ3W++JI1eWHTA6hXgZHecFIc0E547jJwbtTn70UxX6QzwAFus163+j3KJ Zb0UcgxnaOojruQmNOPQsc6F47QRL9F+1kHeKJciVxhV1UPMoVF93dUkhassGHVxl3N9 /KruMtkdxz98BVXZCY8VWL0HB2ybk3mC9gO8yaq6Yn6lWJoocOIwUTaugpeUpDLGmvLL o5h39mCM6sn6c8GF3cuEMrvR7eE573EuO7HYzPSv2Vjtzgr5zmDYL7y9sWTEHQ33AGQ4 Kn0xT2AzgvT06obRqhjb3FLEJ/kmHJNBd+le74lwvBZaw0D9zpsHFquJ1TvgGygxZRG0 j7Xg== 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=f8lrR0ZiQSWaL4KkWmwSgVmShpah+Hqkiq/7u9MC3Ec=; b=lm7tZESYyWTnGmNU1ni3H9TFsXpfqH6M9v7ukgYVuCOo1l6O5j58WCsCR7VJYHDQQN tMHoerwBZrfwBrY1Fxhgy4m4IOi8X46GozhimITCnJTTM7xFgw5z6fjm54LU406iMpiW uC2H2hq42OQUegA2QgRCI+w8c0zIYkQtOVxp+KQ3XbtczSyJOQazp+y2yDIbkJMKGpBU SwqP3tlrqnZgJD1RI1bWsozSGEvcfiotDOb2gy25w2Y0Bqe5BuvxlDFui93FKBybLLE1 CK4EIZ1m5OwJIzLmCtLdgfOIz8aSVAGTndUaEgU+Ofj9vEnjmVJHh+bXEoMa0u3L2PZg 1vOw== X-Gm-Message-State: AOAM533+QLeqrKYRBEt5HaX+Y3tbznp/3Yb2g0tzYKUj3FodJGRfaGdp XnSan07+4wpNeH4KtuBd5wVvBr/sce/Vagk6pgro X-Google-Smtp-Source: ABdhPJyP73PgPrTEn5ZRwI0uF0fAfXgSrG4K8zBx7Ya+smcB67VFKL3uJxgtQS1IadQYI/2VpEQd/iR/G9g05fsqakg= X-Received: by 2002:a05:6402:4314:: with SMTP id m20mr19843171edc.5.1615179017444; Sun, 07 Mar 2021 20:50:17 -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> <44c21bf4-874d-24c9-334b-053c54e8422e@redhat.com> In-Reply-To: <44c21bf4-874d-24c9-334b-053c54e8422e@redhat.com> From: Yongji Xie Date: Mon, 8 Mar 2021 12:50:07 +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 Mon, Mar 8, 2021 at 11:04 AM Jason Wang wrote: > > > On 2021/3/5 4:12 =E4=B8=8B=E5=8D=88, Yongji Xie wrote: > > 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 wr= ote: > >>>>>> 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 = useless > >>>>>>>>> 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_noti= fy() > >>>>>>> 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 us= ed > >>>>> vring's consumer. They will be called one by one in one thread rath= er > >>>>> 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 th= e > >> 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? > > > This kind of 'type' is proposed in the early RFC of vDPA series. One > issue is that at device level, we should not differ virtio from vhost, > so if we introduce that, it might encourge people to design a device > that is dedicated to vhost or virtio which might not be good. > > But we can re-visit this when necessary. > OK, I see. How about adding some information in ops.set_vq_cb()? Thanks, Yongji