Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759392Ab0FJRrB (ORCPT ); Thu, 10 Jun 2010 13:47:01 -0400 Received: from mail.vyatta.com ([76.74.103.46]:34844 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752317Ab0FJRrA (ORCPT ); Thu, 10 Jun 2010 13:47:00 -0400 Date: Thu, 10 Jun 2010 10:46:53 -0700 From: Stephen Hemminger To: Sridhar Samudrala Cc: "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, Rusty Russell , Jiri Pirko , Shirley Ma , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH for-2.6.35] virtio_net: fix oom handling on tx Message-ID: <20100610104653.1aed2ecc@nehalam> In-Reply-To: <1276190227.22064.19.camel@w-sridhar.beaverton.ibm.com> References: <20100610152041.GA3480@redhat.com> <1276190227.22064.19.camel@w-sridhar.beaverton.ibm.com> Organization: Vyatta X-Mailer: Claws Mail 3.7.5 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2525 Lines: 67 On Thu, 10 Jun 2010 10:17:07 -0700 Sridhar Samudrala wrote: > On Thu, 2010-06-10 at 18:20 +0300, Michael S. Tsirkin wrote: > > virtio net will never try to overflow the TX ring, so the only reason > > add_buf may fail is out of memory. Thus, we can not stop the > > device until some request completes - there's no guarantee anything > > at all is outstanding. > > > > Make the error message clearer as well: error here does not > > indicate queue full. > > > > Signed-off-by: Michael S. Tsirkin > > --- > > drivers/net/virtio_net.c | 15 ++++++++------- > > 1 files changed, 8 insertions(+), 7 deletions(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index 85615a3..e48a06f 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -563,7 +563,6 @@ static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev) > > struct virtnet_info *vi = netdev_priv(dev); > > int capacity; > > > > -again: > > /* Free up any pending old buffers before queueing new ones. */ > > free_old_xmit_skbs(vi); > > > > @@ -572,12 +571,14 @@ again: > > > > /* This can happen with OOM and indirect buffers. */ > > if (unlikely(capacity < 0)) { > > - netif_stop_queue(dev); > > - dev_warn(&dev->dev, "Unexpected full queue\n"); > > - if (unlikely(!virtqueue_enable_cb(vi->svq))) { > > - virtqueue_disable_cb(vi->svq); > > - netif_start_queue(dev); > > - goto again; > > + if (net_ratelimit()) { > > + if (likely(capacity == -ENOMEM)) > > + dev_warn(&dev->dev, > > + "TX queue failure: out of memory\n"); > > + else > > + dev_warn(&dev->dev, > > + "Unexpected TX queue failure: %d\n", > > + capacity); > > } > > return NETDEV_TX_BUSY; > > } > > It is not clear to me how xmit_skb() can return -ENOMEM. > xmit_skb() calls virtqueue_add_buf_gfp() which can return -ENOSPC. > Even vring_add_indirect() doesn't return -ENOMEM on kmalloc failure. It makes more sense to have the device increment tx_droppped, and return NETDEV_TX_OK. Skip the message (or make it a pr_debug()). Network devices do not guarantee packet delivery, and if out of resources then holding more data in the queue is going to hurt not help the situation. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/