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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id F1660C7619A for ; Mon, 27 Mar 2023 12:44:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232027AbjC0MoY (ORCPT ); Mon, 27 Mar 2023 08:44:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38594 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229577AbjC0MoW (ORCPT ); Mon, 27 Mar 2023 08:44:22 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 993A43583 for ; Mon, 27 Mar 2023 05:43:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679921013; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=okew6DGjoVJwf2XramfWu6hiLwNPjgMAsie77LgA37k=; b=G8phJLBKC2DZq9v/hM8HFFkXodiEz4v9bWzTJ/ftNjFKmvXN2qPElUWpIFyQ0MrptenbON qFO7xarvxVLEJ2lNvkogPkm1OQFGRLQNJzHkEeR7w3GzoCORnL8Iz4QkhVdzSbTBUzG++B hafhTDD+rQQ1B6yAXtLOYjYjj5LC6s0= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-655-I3xFbgGEOk6GEH1XNHi1ZA-1; Mon, 27 Mar 2023 08:43:32 -0400 X-MC-Unique: I3xFbgGEOk6GEH1XNHi1ZA-1 Received: by mail-wr1-f71.google.com with SMTP id s28-20020adfa29c000000b002d92bb99383so743407wra.23 for ; Mon, 27 Mar 2023 05:43:32 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1679921011; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=okew6DGjoVJwf2XramfWu6hiLwNPjgMAsie77LgA37k=; b=LLMwSslAfkJb3QPpD+1BtENEQ7sVw279EWdlegdE9ERJCAnftP0MTnXXH5aYb6w/F4 8/HetcEVK4n7WJtH/XkOZkUHI+Ph5bqbXU7hRmogpx0vPjcHWGQhl2/RPlihrwe85EDD wP1+m5ZeIFOCLaEGPVTgFiGyCZIE1Tcei78rbVqK7YWbqaO1H9dJ/ebv37kYQPKl9IOj rj4mG5QfIr2kmzV0gJbykWnTA2qJSuS62XFh7Qle2183qAV4lJivc2U1V57dIAuhQNWe X6lHC0/6Wko+c8UTi+LQ0N/AES5MQLQNGJVbAaC8LkzS5LC6QvIChUGOICcADkkoyQLA WtBQ== X-Gm-Message-State: AAQBX9dUtQURp/DWBfuSwdPi3crdpFJQGTBix/Ay7N7q16m+5u5+PxPG ZgH78YULlZGz33kSw1fvywjBRgx2D8fJlkmaRMFVzyKRJ9cx2ZuUeapH6wWZloLgPKKBEcZM53N eCVMdQ8lyY36d3Nd3NU4vwgkE X-Received: by 2002:a7b:c045:0:b0:3ef:6fee:8057 with SMTP id u5-20020a7bc045000000b003ef6fee8057mr1516951wmc.25.1679921011575; Mon, 27 Mar 2023 05:43:31 -0700 (PDT) X-Google-Smtp-Source: AKy350b8/SyqswJ4jRTerw8oSEMPhEZEW1SwIMQQ5198eUS5XRuV+yjc/mQikzsTZrLWNyeSaRuqQQ== X-Received: by 2002:a7b:c045:0:b0:3ef:6fee:8057 with SMTP id u5-20020a7bc045000000b003ef6fee8057mr1516940wmc.25.1679921011227; Mon, 27 Mar 2023 05:43:31 -0700 (PDT) Received: from redhat.com ([2.52.153.142]) by smtp.gmail.com with ESMTPSA id s11-20020a05600c384b00b003edf2ae2432sm8703889wmr.7.2023.03.27.05.43.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Mar 2023 05:43:30 -0700 (PDT) Date: Mon, 27 Mar 2023 08:43:27 -0400 From: "Michael S. Tsirkin" To: Albert Huang Cc: Jason Wang , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] virtio_ring: don't update event idx on get_buf Message-ID: <20230327084248-mutt-send-email-mst@kernel.org> References: <20230325105633.58592-1-huangjie.albert@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230325105633.58592-1-huangjie.albert@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org is the below same as what I posted or different? how? On Sat, Mar 25, 2023 at 06:56:33PM +0800, Albert Huang wrote: > in virtio_net, if we disable the napi_tx, when we triger a tx interrupt, > the vq->event_triggered will be set to true. It will no longer be set to > false. Unless we explicitly call virtqueue_enable_cb_delayed or > virtqueue_enable_cb_prepare. > > If we disable the napi_tx, it will only be called when the tx ring > buffer is relatively small. > > Because event_triggered is true. Therefore, VRING_AVAIL_F_NO_INTERRUPT or > VRING_PACKED_EVENT_FLAG_DISABLE will not be set. So we update > vring_used_event(&vq->split.vring) or vq->packed.vring.driver->off_wrap > every time we call virtqueue_get_buf_ctx. This will bring more interruptions. > > To summarize: > 1) event_triggered was set to true in vring_interrupt() > 2) after this nothing will happen for virtqueue_disable_cb() so > VRING_AVAIL_F_NO_INTERRUPT is not set in avail_flags_shadow > 3) virtqueue_get_buf_ctx_split() will still think the cb is enabled > then it tries to publish new event > > To fix, if event_triggered is set to true, do not update > vring_used_event(&vq->split.vring) or vq->packed.vring.driver->off_wrap > > Tested with iperf: > iperf3 tcp stream: > vm1 -----------------> vm2 > vm2 just receives tcp data stream from vm1, and sends the ack to vm1, > there are many tx interrupts in vm2. > but without event_triggered there are just a few tx interrupts. > > Fixes: 8d622d21d248 ("virtio: fix up virtio_disable_cb") > Signed-off-by: Albert Huang > Message-Id: <20230321085953.24949-1-huangjie.albert@bytedance.com> what is this exactly? > Signed-off-by: Michael S. Tsirkin > --- > drivers/virtio/virtio_ring.c | 6 ++++-- > 1 file changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index cbeeea1b0439..1c36fa477966 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -914,7 +914,8 @@ static void *virtqueue_get_buf_ctx_split(struct virtqueue *_vq, > /* If we expect an interrupt for the next entry, tell host > * by writing event index and flush out the write before > * the read in the next get_buf call. */ > - if (!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT)) > + if (unlikely(!(vq->split.avail_flags_shadow & VRING_AVAIL_F_NO_INTERRUPT) && > + !vq->event_triggered)) > virtio_store_mb(vq->weak_barriers, > &vring_used_event(&vq->split.vring), > cpu_to_virtio16(_vq->vdev, vq->last_used_idx)); > @@ -1744,7 +1745,8 @@ static void *virtqueue_get_buf_ctx_packed(struct virtqueue *_vq, > * by writing event index and flush out the write before > * the read in the next get_buf call. > */ > - if (vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC) > + if (unlikely(vq->packed.event_flags_shadow == VRING_PACKED_EVENT_FLAG_DESC && > + !vq->event_triggered)) > virtio_store_mb(vq->weak_barriers, > &vq->packed.vring.driver->off_wrap, > cpu_to_le16(vq->last_used_idx)); > -- > 2.37.0 (Apple Git-136)