From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EC22326E701 for ; Fri, 12 Sep 2025 08:50:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757667044; cv=none; b=YLcEJkX+Vt82Lv+rBU3qwf4pXyhXA2JeTxPRoDaBRRUYEjyL/rQupPW9z00RxBG1VoPrG/Q1DtitNbZjhk7UbKv1iT5rcNJ89xbcMMT0miuuIqGkILAn+oXpIELAd9BWfQ89FB33RdL0r7O3vMHlSoiTEcplpLO9H1ubDoILvUE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1757667044; c=relaxed/simple; bh=eIehRNox/dG9Q/NjSvCbhxAAOwBQCzMl/Y+73D6b6cs=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UIrWDAfOpV8fHzrQJi1n9e+XJW2kfzGY8b7AsJGix3r6+Gdlkg/7ffPijSJY/oPTb9ibAdzsLhzSaK6B8zmg8aLHW+6erHmQGnu4XRtG0EuEBzH5klxE7qqeaiYqg7ulWsotZCFP2+gmaTOxjgm8cafUJq7Vr+NQNdnu8+JQ0q8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=dw7lbyV1; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="dw7lbyV1" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1757667042; 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=bGhSd8CvNyRTKzq49MHrvoxg5fRG/+TgxZE8XqY/Z/Y=; b=dw7lbyV1uAyUvQeBntax1lqec9je/V7K4z0hn4m+rei4jme5QqeFr5bG+oLLrRnKnxsbic 7dkcHCag5IQEPQgn1An8VEF7XuPUaK30wcATMnsUoiOTzicV9fUFbG6TiGg8aMlTB5g4j9 Y9n49vofSTJyfeOMcJ6W5hjFAp01uu0= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-517-9NHcSGlnMdi-wtWsZ5RS9w-1; Fri, 12 Sep 2025 04:50:40 -0400 X-MC-Unique: 9NHcSGlnMdi-wtWsZ5RS9w-1 X-Mimecast-MFC-AGG-ID: 9NHcSGlnMdi-wtWsZ5RS9w_1757667039 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-3e7691b7dfdso224547f8f.0 for ; Fri, 12 Sep 2025 01:50:40 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1757667039; x=1758271839; 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=bGhSd8CvNyRTKzq49MHrvoxg5fRG/+TgxZE8XqY/Z/Y=; b=plls2ZXiGZZV8EiopSTbKaV0bpZNU9v7xQgNlOSGt07EcbwLYqTnU5J4w9CYwhxafC 3VIxR0dNp3LSri68PQ3f3s12/vbN2xLaEtP2fgkh8vIrGVZ6jz3Ku3YhxIgvTKFFUmkk 1ktPZCdeJwi+FLOluyb6DUCe+SJKSvABXcxXvDRQvtP1oRhVNaJAvu49JVmvzx76/pDO xvtQoGHYrlf6eLu60ki2BbJGsebiuNp5hJ5leDk64Cw1kjtnAuGO8Vdag9SKLfybf9YD JD/mgJ3boqfkM+Z50NJmXY7qFs6Kah4ZGU6wBsXJk6UwdPuRqGTc6cAf4KPrVNa+7rPZ UodA== X-Forwarded-Encrypted: i=1; AJvYcCXEqmlJMYoAWF3LNivh7PnrmKsPz3OA38aSzm/nItu9Po4CQIwxgRsMMiH8p+BzzB6Hb5+C2MQ=@vger.kernel.org X-Gm-Message-State: AOJu0YzZ30K7Jq4ao6+maUsvQ78mfrcwg77IxWKkhUB/+HdxAG8ndYhO p1D+wzhiiqKMakSzVhtJuYxTKNyYjPc7wK3nYHqhm4vbUhxK8KdEtm+0JweVObF8S76/F+sUvfl +ptn9CizCJ7JZpgeuc08e/E1gN6peNeObKnK9xwg1yu+niSAGiyGj2TR1yg== X-Gm-Gg: ASbGncswqoOVCwtRI/xikCSKV9ZiqdtbjELnsxh/aLqq26sEnFnBrBtzU5vdHwIGd/H BwYDzRCRymaT2EZp3vk9F9T9IKo7zP180EQQqz67UtMen5Ukf3Uv/QSAocv5l3xkNzoaSi3b0dw RGGvhT44xMfDMTPiRGx88C+4dSr9S4VFQtDC4vkoIfR3RYAtLOKHrltiO1zjBnPv+xdTjXk+RyH 0Qzzwda0ro9W92xNf65O4IKEi5UBuWRy/odDBPrk1yjBwbgGuGxdfheYl2HVunH469970phCSYl 9IJqwxtgQhz5t86JeOZeKZAVq3bkFZnd X-Received: by 2002:a05:6000:178b:b0:3e7:5f26:f1f3 with SMTP id ffacd0b85a97d-3e7658c0f20mr1991855f8f.25.1757667039439; Fri, 12 Sep 2025 01:50:39 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGS2Tz/SulTKIR1f9nSWXhOdRDsMn29o7jRrHZHGh4hg8LiyfPRYgIJgThyJhmqJvpcfuVOUA== X-Received: by 2002:a05:6000:178b:b0:3e7:5f26:f1f3 with SMTP id ffacd0b85a97d-3e7658c0f20mr1991827f8f.25.1757667038953; Fri, 12 Sep 2025 01:50:38 -0700 (PDT) Received: from redhat.com ([2a0d:6fc0:1536:c800:2952:74e:d261:8021]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7b42bdc5asm321061f8f.21.2025.09.12.01.50.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 12 Sep 2025 01:50:38 -0700 (PDT) Date: Fri, 12 Sep 2025 04:50:35 -0400 From: "Michael S. Tsirkin" To: Jason Wang Cc: eperezma@redhat.com, jonah.palmer@oracle.com, kuba@kernel.org, jon@nutanix.com, kvm@vger.kernel.org, virtualization@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH net 2/2] vhost-net: correctly flush batched packet before enabling notification Message-ID: <20250912044523-mutt-send-email-mst@kernel.org> References: <20250912082658.2262-1-jasowang@redhat.com> <20250912082658.2262-2-jasowang@redhat.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250912082658.2262-2-jasowang@redhat.com> On Fri, Sep 12, 2025 at 04:26:58PM +0800, Jason Wang wrote: > Commit 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after > sendmsg") tries to defer the notification enabling by moving the logic > out of the loop after the vhost_tx_batch() when nothing new is > spotted. This will bring side effects as the new logic would be reused > for several other error conditions. > > One example is the IOTLB: when there's an IOTLB miss, get_tx_bufs() > might return -EAGAIN and exit the loop and see there's still available > buffers, so it will queue the tx work again until userspace feed the > IOTLB entry correctly. This will slowdown the tx processing and may > trigger the TX watchdog in the guest. It's not that it might. Pls clarify that it *has been reported* to do exactly that, and add a link to the report. > Fixing this by stick the notificaiton enabling logic inside the loop > when nothing new is spotted and flush the batched before. > > Reported-by: Jon Kohler > Cc: stable@vger.kernel.org > Fixes: 8c2e6b26ffe2 ("vhost/net: Defer TX queue re-enable until after sendmsg") > Signed-off-by: Jason Wang So this is mostly a revert, but with vhost_tx_batch(net, nvq, sock, &msg); added in to avoid regressing performance. If you do not want to structure it like this (revert+optimization), then pls make that clear in the message. > --- > drivers/vhost/net.c | 33 +++++++++++++-------------------- > 1 file changed, 13 insertions(+), 20 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 16e39f3ab956..3611b7537932 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -765,11 +765,11 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock) > int err; > int sent_pkts = 0; > bool sock_can_batch = (sock->sk->sk_sndbuf == INT_MAX); > - bool busyloop_intr; > bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER); > > do { > - busyloop_intr = false; > + bool busyloop_intr = false; > + > if (nvq->done_idx == VHOST_NET_BATCH) > vhost_tx_batch(net, nvq, sock, &msg); > > @@ -780,10 +780,18 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock) > break; > /* Nothing new? Wait for eventfd to tell us they refilled. */ > if (head == vq->num) { > - /* Kicks are disabled at this point, break loop and > - * process any remaining batched packets. Queue will > - * be re-enabled afterwards. > + /* Flush batched packets before enabling > + * virqtueue notification to reduce > + * unnecssary virtqueue kicks. typos: virtqueue, unnecessary > */ > + vhost_tx_batch(net, nvq, sock, &msg); > + if (unlikely(busyloop_intr)) { > + vhost_poll_queue(&vq->poll); > + } else if (unlikely(vhost_enable_notify(&net->dev, > + vq))) { > + vhost_disable_notify(&net->dev, vq); > + continue; > + } > break; > } > > @@ -839,22 +847,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock) > ++nvq->done_idx; > } while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len))); > > - /* Kicks are still disabled, dispatch any remaining batched msgs. */ > vhost_tx_batch(net, nvq, sock, &msg); > - > - if (unlikely(busyloop_intr)) > - /* If interrupted while doing busy polling, requeue the > - * handler to be fair handle_rx as well as other tasks > - * waiting on cpu. > - */ > - vhost_poll_queue(&vq->poll); > - else > - /* All of our work has been completed; however, before > - * leaving the TX handler, do one last check for work, > - * and requeue handler if necessary. If there is no work, > - * queue will be reenabled. > - */ > - vhost_net_busy_poll_try_queue(net, vq); > } > > static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock) > -- > 2.34.1