Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759275Ab1FBDzk (ORCPT ); Wed, 1 Jun 2011 23:55:40 -0400 Received: from ozlabs.org ([203.10.76.45]:40100 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752148Ab1FBDzg (ORCPT ); Wed, 1 Jun 2011 23:55:36 -0400 From: Rusty Russell To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Carsten Otte , Christian Borntraeger , linux390@de.ibm.com, Martin Schwidefsky , Heiko Carstens , Shirley Ma , lguest@lists.ozlabs.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-s390@vger.kernel.org, kvm@vger.kernel.org, Krishna Kumar , Tom Lendacky , steved@us.ibm.com, habanero@linux.vnet.ibm.com Subject: Re: [PATCH RFC 2/3] virtio_net: fix tx capacity checks using new API In-Reply-To: <110045d5bf250e6ed9c739f8cc6adbbf54e3cc9c.1306921434.git.mst@redhat.com> References: <110045d5bf250e6ed9c739f8cc6adbbf54e3cc9c.1306921434.git.mst@redhat.com> User-Agent: Notmuch/0.5 (http://notmuchmail.org) Emacs/23.2.1 (i686-pc-linux-gnu) Date: Thu, 02 Jun 2011 11:40:26 +0930 Message-ID: <87vcwphtkd.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 931 Lines: 21 On Wed, 1 Jun 2011 12:49:54 +0300, "Michael S. Tsirkin" wrote: > In the (rare) case where new descriptors are used > while virtio_net enables vq callback for the TX vq, > virtio_net uses the number of sg entries in the skb it frees to > calculate how many descriptors in the ring have just been made > available. But this value is an overestimate: with indirect buffers > each skb only uses one descriptor entry, meaning we may wake the queue > only to find we still can't transmit anything. This is a bit misleading. The value is an overestimate, but so is the requirement for 2+MAX_SKB_FRAGS, *unless* we suddenly drop into direct mode due to OOM. Thanks, Rusty. -- 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/