Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753873AbbDNJ6n (ORCPT ); Tue, 14 Apr 2015 05:58:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37729 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752433AbbDNJ6g (ORCPT ); Tue, 14 Apr 2015 05:58:36 -0400 Date: Tue, 14 Apr 2015 11:58:32 +0200 From: "Michael S. Tsirkin" To: Cornelia Huck Cc: Rusty Russell , linux-kernel@vger.kernel.org, Pawel Moll , virtio-dev@lists.oasis-open.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCH v3 0/6] virtio_balloon: virtio 1 support Message-ID: <20150414115440-mutt-send-email-mst@redhat.com> References: <1427884468-23930-1-git-send-email-mst@redhat.com> <20150412170141-mutt-send-email-mst@redhat.com> <87h9sjtsvb.fsf@rustcorp.com.au> <20150414102438.11d12347.cornelia.huck@de.ibm.com> <20150414103036-mutt-send-email-mst@redhat.com> <20150414115053.78189c71.cornelia.huck@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150414115053.78189c71.cornelia.huck@de.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5668 Lines: 170 On Tue, Apr 14, 2015 at 11:50:53AM +0200, Cornelia Huck wrote: > On Tue, 14 Apr 2015 11:21:11 +0200 > "Michael S. Tsirkin" wrote: > > > diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h > > index f81b220..164e0c2 100644 > > --- a/include/uapi/linux/virtio_balloon.h > > +++ b/include/uapi/linux/virtio_balloon.h > > @@ -52,15 +52,31 @@ struct virtio_balloon_config { > > #define VIRTIO_BALLOON_S_MEMTOT 5 /* Total amount of memory */ > > #define VIRTIO_BALLOON_S_NR 6 > > > > +/* > > + * Memory statistics structure. > > + * Driver fills an array of these structures and passes to device. > > + * > > + * NOTE: fields are laid out in a way that would make compiler add padding > > + * between and after fields, so we have to use compiler-specific attributes to > > + * pack it, to disable this padding. This also often causes compiler to > > + * generate suboptimal code. > > + * > > + * We maintain this for backwards compatibility, but don't follow this example. > > s/this/the existing statistics structure/ existing seems redundant. What else? non-existing? > > + * > > + * Do something like the below instead: > > If you want to implement a similar structure, do... > > Just that nobody gets the idea that they are supposed to implement new > balloon statistics ;) > > > + * struct virtio_balloon_stat { > > + * __virtio16 tag; > > + * __u8 reserved[6]; > > + * __virtio64 val; > > + * }; > > (...) > > > @@ -225,13 +219,8 @@ static inline void update_stat(struct virtio_balloon *vb, int idx, > > u16 tag, u64 val) > > { > > BUG_ON(idx >= VIRTIO_BALLOON_S_NR); > > - if (virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1)) { > > - vb->stats[idx].tag = cpu_to_le32(tag); > > - vb->stats[idx].val = cpu_to_le64(val); > > - } else { > > - vb->legacy_stats[idx].tag = tag; > > - vb->legacy_stats[idx].val = val; > > - } > > + vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag); > > Seems that nobody seemed to care much about statistics... Or about BE guests ;) > > + vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val); > > } > > > > #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT) > > > > With these changes merged in: > > Acked-by: Cornelia Huck OK, here's an updated incremental patch: only comment changed. diff --git a/include/uapi/linux/virtio_balloon.h b/include/uapi/linux/virtio_balloon.h index f81b220..984169a 100644 --- a/include/uapi/linux/virtio_balloon.h +++ b/include/uapi/linux/virtio_balloon.h @@ -52,15 +52,32 @@ struct virtio_balloon_config { #define VIRTIO_BALLOON_S_MEMTOT 5 /* Total amount of memory */ #define VIRTIO_BALLOON_S_NR 6 +/* + * Memory statistics structure. + * Driver fills an array of these structures and passes to device. + * + * NOTE: fields are laid out in a way that would make compiler add padding + * between and after fields, so we have to use compiler-specific attributes to + * pack it, to disable this padding. This also often causes compiler to + * generate suboptimal code. + * + * We maintain this statistics structure format for backwards compatibility, + * but don't follow this example. + * + * If implementing a similar structure, do something like the below instead: + * struct virtio_balloon_stat { + * __virtio16 tag; + * __u8 reserved[6]; + * __virtio64 val; + * }; + * + * In other words, add explicit reserved fields to align field and + * structure boundaries at field size, avoiding compiler padding + * without the packed attribute. + */ struct virtio_balloon_stat { - __u16 tag; - __u64 val; + __virtio16 tag; + __virtio64 val; } __attribute__((packed)); -struct virtio_balloon_stat_modern { - __le16 tag; - __u8 reserved[6]; - __le64 val; -}; - #endif /* _LINUX_VIRTIO_BALLOON_H */ diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c index 0583720..9db546e 100644 --- a/drivers/virtio/virtio_balloon.c +++ b/drivers/virtio/virtio_balloon.c @@ -77,10 +77,7 @@ struct virtio_balloon { /* Memory statistics */ int need_stats_update; - union { - struct virtio_balloon_stat_modern stats[VIRTIO_BALLOON_S_NR]; - struct virtio_balloon_stat legacy_stats[VIRTIO_BALLOON_S_NR]; - }; + struct virtio_balloon_stat stats[VIRTIO_BALLOON_S_NR]; /* To register callback in oom notifier call chain */ struct notifier_block nb; @@ -93,10 +90,7 @@ static struct virtio_device_id id_table[] = { static void stats_sg_init(struct virtio_balloon *vb, struct scatterlist *sg) { - if (virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1)) - sg_init_one(sg, vb->stats, sizeof(vb->stats)); - else - sg_init_one(sg, vb->legacy_stats, sizeof(vb->legacy_stats)); + sg_init_one(sg, vb->stats, sizeof(vb->stats)); } static u32 page_to_balloon_pfn(struct page *page) @@ -225,13 +219,8 @@ static inline void update_stat(struct virtio_balloon *vb, int idx, u16 tag, u64 val) { BUG_ON(idx >= VIRTIO_BALLOON_S_NR); - if (virtio_has_feature(vb->vdev, VIRTIO_F_VERSION_1)) { - vb->stats[idx].tag = cpu_to_le32(tag); - vb->stats[idx].val = cpu_to_le64(val); - } else { - vb->legacy_stats[idx].tag = tag; - vb->legacy_stats[idx].val = val; - } + vb->stats[idx].tag = cpu_to_virtio16(vb->vdev, tag); + vb->stats[idx].val = cpu_to_virtio64(vb->vdev, val); } #define pages_to_bytes(x) ((u64)(x) << PAGE_SHIFT) -- 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/