From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 A108B26657B for ; Wed, 17 Sep 2025 06:31:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758090675; cv=none; b=YqRsa5+1BACLy0zUhMVdV8xsqiolwwQmz/Of+slSEEmBcQbtgotRm/GPcCtdTuEdO8p2DMNco8UIAEJM1VWDGZt70x/Klwhdggo2HJj5nYZvU550kaXtD1XSbR20MiVaxO6vMSJ3QXfnjXXJ8F7LMKJ1e1d5ix9wKQgG+C7Ejm4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758090675; c=relaxed/simple; bh=+tg+zqIGYZeJAtI0BLNvB8hvQjoSALLxLiAiqbcrHlo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=jzUc4tW6yXz+gaeL2rH9HVtoL84HaESfRAtHH4oBZ2b0IlzmRcq7uuOzeESGvAyQrffOEtWh/yAgQyEyiCjHXVoTa28JU/JScreuAhBhvQWtE+0IOyQTkfCSwkdh41YTM4febTTNor1DODx8dVu907xr/hPoQvoRiXqE/HBmThI= 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=U3cNV2Vw; arc=none smtp.client-ip=170.10.133.124 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="U3cNV2Vw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758090672; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Hv1+QMwOCvl16zguKyuS6dehju0VZPoXK59mfGqtUlY=; b=U3cNV2VwB76mplWEfdsDKZLoePuIYzxoDadrfwqzO76xQlBiuPd0glwtjJHOXcciWtFJEX nw0C6imrGkdqMod8nhA8KWx0GZ1ufe0tA9lSCKqIfdmg2wmVt6TjRuQTCvGQSz/SqmdvGg Tkv7ca1AUOjm0rgoMHEz6t0uAbGlTUc= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-404-mL9TLt2sOzunTe7Y-TesNg-1; Wed, 17 Sep 2025 02:31:08 -0400 X-MC-Unique: mL9TLt2sOzunTe7Y-TesNg-1 X-Mimecast-MFC-AGG-ID: mL9TLt2sOzunTe7Y-TesNg_1758090667 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3E198195608E; Wed, 17 Sep 2025 06:31:07 +0000 (UTC) Received: from localhost.localdomain (unknown [10.72.112.239]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 187851955F2D; Wed, 17 Sep 2025 06:31:01 +0000 (UTC) From: Jason Wang To: mst@redhat.com, jasowang@redhat.com, eperezma@redhat.com Cc: 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: [PATCH vhost 2/3] Revert "vhost/net: Defer TX queue re-enable until after sendmsg" Date: Wed, 17 Sep 2025 14:30:44 +0800 Message-ID: <20250917063045.2042-2-jasowang@redhat.com> In-Reply-To: <20250917063045.2042-1-jasowang@redhat.com> References: <20250917063045.2042-1-jasowang@redhat.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 This reverts commit 8c2e6b26ffe243be1e78f5a4bfb1a857d6e6f6d6. It 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 trigger the TX watchdog in the guest as reported in https://lkml.org/lkml/2025/9/10/1596. To fix, revert the change. A follow up patch will being the performance back in a safe way. 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 Signed-off-by: Michael S. Tsirkin --- drivers/vhost/net.c | 30 +++++++++--------------------- 1 file changed, 9 insertions(+), 21 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 16e39f3ab956..57efd5c55f89 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 +780,13 @@ 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. - */ + 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 +842,7 @@ 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