From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43117) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1fQPPY-00066x-EZ for qemu-devel@nongnu.org; Tue, 05 Jun 2018 23:47:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1fQPPT-0001HQ-JO for qemu-devel@nongnu.org; Tue, 05 Jun 2018 23:47:00 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:42364 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1fQPPT-0001HG-DS for qemu-devel@nongnu.org; Tue, 05 Jun 2018 23:46:55 -0400 References: <1528225683-11413-1-git-send-email-wexu@redhat.com> <1528225683-11413-8-git-send-email-wexu@redhat.com> From: Jason Wang Message-ID: Date: Wed, 6 Jun 2018 11:46:48 +0800 MIME-Version: 1.0 In-Reply-To: <1528225683-11413-8-git-send-email-wexu@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [RFC v2 7/8] virtio: event suppression for packed ring List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: wexu@redhat.com, qemu-devel@nongnu.org Cc: jfreimann@redhat.com, tiwei.bie@intel.com, mst@redhat.com On 2018=E5=B9=B406=E6=9C=8806=E6=97=A5 03:08, wexu@redhat.com wrote: > From: Wei Xu > > Signed-off-by: Wei Xu > Signed-off-by: Wei Xu Duplicated. > --- > hw/virtio/virtio.c | 115 ++++++++++++++++= +++++++-- > include/standard-headers/linux/virtio_config.h | 13 +++ > 2 files changed, 119 insertions(+), 9 deletions(-) > > diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c > index 6f2da83..4543974 100644 > --- a/hw/virtio/virtio.c > +++ b/hw/virtio/virtio.c > @@ -226,6 +226,24 @@ static void vring_desc_read(VirtIODevice *vdev, VR= ingDesc *desc, > virtio_tswap16s(vdev, &desc->next); > } > =20 > +static void vring_packed_event_read(VirtIODevice *vdev, > + MemoryRegionCache *cache, VRingPackedDescE= vent *e) > +{ > + address_space_read_cached(cache, 0, e, sizeof(*e)); > + virtio_tswap16s(vdev, &e->off_wrap); > + virtio_tswap16s(vdev, &e->flags); You need to make sure flags is read before off_wrap. > +} > + > +static void vring_packed_event_write(VirtIODevice *vdev, > + MemoryRegionCache *cache, VRingPackedDescE= vent *e) > +{ > + virtio_tswap16s(vdev, &e->off_wrap); > + virtio_tswap16s(vdev, &e->flags); > + address_space_write_cached(cache, 0, e, sizeof(*e)); You need make sure flags were wrote before off_wrap. > + address_space_cache_invalidate(cache, 0, sizeof(VRingUsedElem)); > +} > + > + > static VRingMemoryRegionCaches *vring_get_region_caches(struct VirtQu= eue *vq) > { > VRingMemoryRegionCaches *caches =3D atomic_rcu_read(&vq->vring.ca= ches); > @@ -332,14 +350,8 @@ static inline void vring_set_avail_event(VirtQueue= *vq, uint16_t val) > address_space_cache_invalidate(&caches->used, pa, sizeof(val)); > } > =20 > -void virtio_queue_set_notification(VirtQueue *vq, int enable) > +static void virtio_queue_set_notification_split(VirtQueue *vq, int ena= ble) > { > - vq->notification =3D enable; > - > - if (!vq->vring.desc) { > - return; > - } > - > rcu_read_lock(); > if (virtio_vdev_has_feature(vq->vdev, VIRTIO_RING_F_EVENT_IDX)) { > vring_set_avail_event(vq, vring_avail_idx(vq)); > @@ -355,6 +367,38 @@ void virtio_queue_set_notification(VirtQueue *vq, = int enable) > rcu_read_unlock(); > } > =20 > +static void virtio_queue_set_notification_packed(VirtQueue *vq, int en= able) > +{ > + VRingPackedDescEvent e; > + VRingMemoryRegionCaches *caches; > + > + rcu_read_lock(); > + caches =3D vring_get_region_caches(vq); > + vring_packed_event_read(vq->vdev, &caches->device, &e); Why need read? > + if (enable) { > + e.flags =3D RING_EVENT_FLAGS_ENABLE; > + } else { > + e.flags =3D RING_EVENT_FLAGS_DISABLE; > + } > + vring_packed_event_write(vq->vdev, &caches->device, &e); > + rcu_read_unlock(); > +} > + > +void virtio_queue_set_notification(VirtQueue *vq, int enable) > +{ > + vq->notification =3D enable; > + > + if (!vq->vring.desc) { > + return; > + } > + > + if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) { > + virtio_queue_set_notification_packed(vq, enable); > + } else { > + virtio_queue_set_notification_split(vq, enable); > + } > +} > + > int virtio_queue_ready(VirtQueue *vq) > { > return vq->vring.avail !=3D 0; > @@ -2059,8 +2103,7 @@ static void virtio_set_isr(VirtIODevice *vdev, in= t value) > } > } > =20 > -/* Called within rcu_read_lock(). */ > -static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq) > +static bool virtio_split_should_notify(VirtIODevice *vdev, VirtQueue *= vq) > { > uint16_t old, new; > bool v; > @@ -2083,6 +2126,60 @@ static bool virtio_should_notify(VirtIODevice *v= dev, VirtQueue *vq) > return !v || vring_need_event(vring_get_used_event(vq), new, old)= ; > } > =20 > +static bool vring_packed_need_event(VirtQueue *vq, uint16_t off_wrap, > + uint16_t new, uint16_t old) > +{ > + bool wrap =3D vq->used_wrap_counter; > + int off =3D off_wrap & ~(1 << 15); > + > + if (new < old) { > + new +=3D vq->vring.num; > + wrap ^=3D 1; > + } > + > + if (wrap !=3D off_wrap >> 15) { > + off +=3D vq->vring.num; > + } > + > + return vring_need_event(off, new, old); > +} > + > +static bool virtio_packed_should_notify(VirtIODevice *vdev, VirtQueue = *vq) > +{ > + VRingPackedDescEvent e; > + uint16_t old, new; > + bool v; > + VRingMemoryRegionCaches *caches; > + > + caches =3D vring_get_region_caches(vq); > + vring_packed_event_read(vdev, &caches->driver, &e); > + > + /* Make sure we see the updated flags */ > + smp_mb(); Like I mention several times, why need a memory barrier here? > + if (e.flags =3D=3D RING_EVENT_FLAGS_DISABLE) { > + return false; > + } else if (e.flags =3D=3D RING_EVENT_FLAGS_ENABLE) { > + return true; > + } > + > + v =3D vq->signalled_used_valid; > + vq->signalled_used_valid =3D true; > + old =3D vq->signalled_used; > + new =3D vq->signalled_used =3D vq->used_idx; > + > + return !v || vring_packed_need_event(vq, e.off_wrap, new, old); > +} > + > +/* Called within rcu_read_lock(). */ > +static bool virtio_should_notify(VirtIODevice *vdev, VirtQueue *vq) > +{ > + if (virtio_vdev_has_feature(vdev, VIRTIO_F_RING_PACKED)) { > + return virtio_packed_should_notify(vdev, vq); > + } else { > + return virtio_split_should_notify(vdev, vq); > + } > +} > + > void virtio_notify_irqfd(VirtIODevice *vdev, VirtQueue *vq) > { > bool should_notify; > diff --git a/include/standard-headers/linux/virtio_config.h b/include/s= tandard-headers/linux/virtio_config.h > index 6ee5529..53e5c83 100644 > --- a/include/standard-headers/linux/virtio_config.h > +++ b/include/standard-headers/linux/virtio_config.h > @@ -73,4 +73,17 @@ > #define VIRTIO_F_IOMMU_PLATFORM 33 > =20 > #define VIRTIO_F_RING_PACKED 34 > + > +/* Enable events */ > +#define RING_EVENT_FLAGS_ENABLE 0x0 > +/* Disable events */ > +#define RING_EVENT_FLAGS_DISABLE 0x1 > +/* > + * * Enable events for a specific descriptor > + * * (as specified by Descriptor Ring Change Event Offset/Wrap Count= er). > + * * Only valid if VIRTIO_F_RING_EVENT_IDX has been negotiated. > + * */ > +#define RING_EVENT_FLAGS_DESC 0x2 > +/* The value 0x3 is reserved */ > + > #endif /* _LINUX_VIRTIO_CONFIG_H */ This could be done in a patch of header sync. Thanks