From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755997Ab1EQQ14 (ORCPT ); Tue, 17 May 2011 12:27:56 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:56675 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755722Ab1EQQ1y (ORCPT ); Tue, 17 May 2011 12:27:54 -0400 From: Tom Lendacky Organization: IBM Linux Performance To: Rusty Russell Subject: Re: [PATCH 09/18] virtio: use avail_event index Date: Tue, 17 May 2011 11:23:32 -0500 User-Agent: KMail/1.13.7 (Linux/2.6.35.13-91.fc14.i686.PAE; KDE/4.6.2; i686; ; ) Cc: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org, 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 , steved@us.ibm.com, habanero@linux.vnet.ibm.com References: <20110515135541.GF24932@redhat.com> <87ei3zdsq2.fsf@rustcorp.com.au> In-Reply-To: <87ei3zdsq2.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201105171123.34706.tahm@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday, May 16, 2011 02:12:21 AM Rusty Russell wrote: > On Sun, 15 May 2011 16:55:41 +0300, "Michael S. Tsirkin" wrote: > > On Mon, May 09, 2011 at 02:03:26PM +0930, Rusty Russell wrote: > > > On Wed, 4 May 2011 23:51:47 +0300, "Michael S. Tsirkin" wrote: > > > > Use the new avail_event feature to reduce the number > > > > of exits from the guest. > > > > > > Figures here would be nice :) > > > > You mean ASCII art in comments? > > I mean benchmarks of some kind. I'm working on getting some benchmark results for the patches. I should hopefully have something in the next day or two. Tom > > > > > @@ -228,6 +237,12 @@ add_head: > > > > * new available array entries. */ > > > > > > > > virtio_wmb(); > > > > vq->vring.avail->idx++; > > > > > > > > + /* If the driver never bothers to kick in a very long while, > > > > + * avail index might wrap around. If that happens, invalidate > > > > + * kicked_avail index we stored. TODO: make sure all drivers > > > > + * kick at least once in 2^16 and remove this. */ > > > > + if (unlikely(vq->vring.avail->idx == vq->kicked_avail)) > > > > + vq->kicked_avail_valid = true; > > > > > > If they don't, they're already buggy. Simply do: > > > WARN_ON(vq->vring.avail->idx == vq->kicked_avail); > > > > Hmm, but does it say that somewhere? > > AFAICT it's a corollary of: > 1) You have a finite ring of size <= 2^16. > 2) You need to kick the other side once you've done some work. > > > > > @@ -482,6 +517,8 @@ void vring_transport_features(struct > > > > virtio_device *vdev) > > > > > > > > break; > > > > > > > > case VIRTIO_RING_F_USED_EVENT_IDX: > > > > break; > > > > > > > > + case VIRTIO_RING_F_AVAIL_EVENT_IDX: > > > > + break; > > > > > > > > default: > > > > /* We don't understand this bit. */ > > > > clear_bit(i, vdev->features); > > > > > > Does this belong in a prior patch? > > > > > > Thanks, > > > Rusty. > > > > Well if we don't support the feature in the ring we should not > > ack the feature, right? > > Ah, you're right. > > Thanks, > Rusty. > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html