Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755280Ab1FHAqE (ORCPT ); Tue, 7 Jun 2011 20:46:04 -0400 Received: from ozlabs.org ([203.10.76.45]:54925 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754013Ab1FHAqB (ORCPT ); Tue, 7 Jun 2011 20:46:01 -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, 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: [PATCHv2 RFC 4/4] Revert "virtio: make add_buf return capacity remaining: In-Reply-To: <20110607155457.GA17436@redhat.com> References: <7572d6fb81181e349af4a8b203ea0977f6e91ae1.1307029009.git.mst@redhat.com> <20110607155457.GA17436@redhat.com> User-Agent: Notmuch/0.5 (http://notmuchmail.org) Emacs/23.2.1 (i686-pc-linux-gnu) Date: Wed, 08 Jun 2011 09:49:56 +0930 Message-ID: <877h8xgonn.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: 1694 Lines: 52 On Tue, 7 Jun 2011 18:54:57 +0300, "Michael S. Tsirkin" wrote: > On Thu, Jun 02, 2011 at 06:43:25PM +0300, Michael S. Tsirkin wrote: > > This reverts commit 3c1b27d5043086a485f8526353ae9fe37bfa1065. > > The only user was virtio_net, and it switched to > > min_capacity instead. > > > > Signed-off-by: Michael S. Tsirkin > > It turns out another place in virtio_net: receive > buf processing - relies on the old behaviour: > > try_fill_recv: > do { > if (vi->mergeable_rx_bufs) > err = add_recvbuf_mergeable(vi, gfp); > else if (vi->big_packets) > err = add_recvbuf_big(vi, gfp); > else > err = add_recvbuf_small(vi, gfp); > > oom = err == -ENOMEM; > if (err < 0) > break; > ++vi->num; > } while (err > 0); > > The point is to avoid allocating a buf if > the ring is out of space and we are sure > add_buf will fail. > > It works well for mergeable buffers and for big > packets if we are not OOM. small packets and > oom will do extra get_page/put_page calls > (but maybe we don't care). > > So this is RX, I intend to drop it from this patchset and focus on the > TX side for starters. We could do some hack where we get the capacity, and estimate how many packets we need to fill it, then try to do that many. I say hack, because knowing whether we're doing indirect buffers is a layering violation. But that's life when you're trying to do microoptimizations. Cheers, 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/