Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759737Ab0FJTJY (ORCPT ); Thu, 10 Jun 2010 15:09:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11551 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759674Ab0FJTJW (ORCPT ); Thu, 10 Jun 2010 15:09:22 -0400 Date: Thu, 10 Jun 2010 22:03:43 +0300 From: "Michael S. Tsirkin" To: Stephen Hemminger Cc: Sridhar Samudrala , 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: <20100610190343.GC4044@redhat.com> References: <20100610152041.GA3480@redhat.com> <1276190227.22064.19.camel@w-sridhar.beaverton.ibm.com> <20100610104653.1aed2ecc@nehalam> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100610104653.1aed2ecc@nehalam> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2942 Lines: 76 On Thu, Jun 10, 2010 at 10:46:53AM -0700, Stephen Hemminger wrote: > 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. > > -- Well, I only keep the existing behaviour around. The changes you propose would be 2.6.36 material. I have it on my todo list to look for a way to test performance under GFP_ATOMIC failure scenario. Any suggestions? -- MST -- 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/