[v4,2/2] virtio: one way barrier for packed vring desc used flags
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Commit Message
In case VIRTIO_F_ORDER_PLATFORM(36) is not negotiated, then the frontend
and backend are assumed to be implemented in software, that is they can
run on identical CPUs in an SMP configuration.
Thus a weak form of memory barriers like rte_smp_r/wmb, other than
rte_cio_r/wmb, is sufficient for this case(vq->hw->weak_barriers == 1)
and yields better performance.
For the above case, this patch helps yielding even better performance
by replacing the two-way barriers with C11 one-way barriers for used
flags in packed ring.
Signed-off-by: Joyce Kong <joyce.kong@arm.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
drivers/net/virtio/virtio_rxtx.c | 12 +++++++---
drivers/net/virtio/virtio_user/virtio_user_dev.c | 4 ++--
drivers/net/virtio/virtqueue.h | 28 +++++++++++++++++++++++-
lib/librte_vhost/virtio_net.c | 5 ++---
4 files changed, 40 insertions(+), 9 deletions(-)
Comments
Hi Joyce,
I test performance impact of your patch set with code base commit id: d03d8622db48918d14bfe805641b1766ecc40088, after applying your v4 patch set , packed ring shows small performance drop as below:
PVP vhost/virtio 1c1q test commit:d03d8622db48918 apply v4 patch set
pvp_virtio11_mergeable 7.218 7.147
pvp_virtio11_normal 7.217 7.182
Thanks,
Yinan
> -----Original Message-----
> From: Joyce Kong [mailto:joyce.kong@arm.com]
> Sent: 2019年9月17日 13:28
> To: dev@dpdk.org
> Cc: nd@arm.com; maxime.coquelin@redhat.com; Wang, Yinan
> <yinan.wang@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>; Bie,
> Tiwei <tiwei.bie@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>;
> amorenoz@redhat.com; Wang, Xiao W <xiao.w.wang@intel.com>; Liu, Yong
> <yong.liu@intel.com>; jfreimann@redhat.com; honnappa.nagarahalli@arm.com;
> gavin.hu@arm.com
> Subject: [PATCH v4 2/2] virtio: one way barrier for packed vring desc used flags
>
> In case VIRTIO_F_ORDER_PLATFORM(36) is not negotiated, then the frontend
> and backend are assumed to be implemented in software, that is they can run on
> identical CPUs in an SMP configuration.
> Thus a weak form of memory barriers like rte_smp_r/wmb, other than
> rte_cio_r/wmb, is sufficient for this case(vq->hw->weak_barriers == 1) and
> yields better performance.
> For the above case, this patch helps yielding even better performance by
> replacing the two-way barriers with C11 one-way barriers for used flags in packed
> ring.
>
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Phil Yang <phil.yang@arm.com>
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
> drivers/net/virtio/virtio_rxtx.c | 12 +++++++---
> drivers/net/virtio/virtio_user/virtio_user_dev.c | 4 ++--
> drivers/net/virtio/virtqueue.h | 28
> +++++++++++++++++++++++-
> lib/librte_vhost/virtio_net.c | 5 ++---
> 4 files changed, 40 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> index a87ffe1..2f0879c 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -122,9 +122,11 @@ virtqueue_dequeue_burst_rx_packed(struct virtqueue
> *vq,
>
> for (i = 0; i < num; i++) {
> used_idx = vq->vq_used_cons_idx;
> + /* desc_is_used has a load-acquire or rte_cio_rmb inside
> + * and wait for used desc in virtqueue.
> + */
> if (!desc_is_used(&desc[used_idx], vq))
> return i;
> - virtio_rmb(vq->hw->weak_barriers);
> len[i] = desc[used_idx].len;
> id = desc[used_idx].id;
> cookie = (struct rte_mbuf *)vq->vq_descx[id].cookie; @@ -233,8
> +235,10 @@ virtio_xmit_cleanup_inorder_packed(struct virtqueue *vq, int num)
> struct vq_desc_extra *dxp;
>
> used_idx = vq->vq_used_cons_idx;
> + /* desc_is_used has a load-acquire or rte_cio_rmb inside
> + * and wait for used desc in virtqueue.
> + */
> while (num > 0 && desc_is_used(&desc[used_idx], vq)) {
> - virtio_rmb(vq->hw->weak_barriers);
> id = desc[used_idx].id;
> do {
> curr_id = used_idx;
> @@ -265,8 +269,10 @@ virtio_xmit_cleanup_normal_packed(struct virtqueue
> *vq, int num)
> struct vq_desc_extra *dxp;
>
> used_idx = vq->vq_used_cons_idx;
> + /* desc_is_used has a load-acquire or rte_cio_rmb inside
> + * and wait for used desc in virtqueue.
> + */
> while (num-- && desc_is_used(&desc[used_idx], vq)) {
> - virtio_rmb(vq->hw->weak_barriers);
> id = desc[used_idx].id;
> dxp = &vq->vq_descx[id];
> vq->vq_used_cons_idx += dxp->ndescs;
> diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c
> b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> index 7911c39..1c575d0 100644
> --- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
> +++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> @@ -698,8 +698,8 @@ virtio_user_handle_cq_packed(struct virtio_user_dev
> *dev, uint16_t queue_idx)
> if (vq->used_wrap_counter)
> flags |= VRING_PACKED_DESC_F_AVAIL_USED;
>
> - rte_smp_wmb();
> - vring->desc[vq->used_idx].flags = flags;
> + __atomic_store_n(&vring->desc[vq->used_idx].flags, flags,
> + __ATOMIC_RELEASE);
>
> vq->used_idx += n_descs;
> if (vq->used_idx >= dev->queue_size) { diff --git
> a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h index
> b728ff8..8d7f197 100644
> --- a/drivers/net/virtio/virtqueue.h
> +++ b/drivers/net/virtio/virtqueue.h
> @@ -54,6 +54,32 @@ virtio_wmb(uint8_t weak_barriers)
> rte_cio_wmb();
> }
>
> +static inline uint16_t
> +virtqueue_fetch_flags_packed(struct vring_packed_desc *dp,
> + uint8_t weak_barriers)
> +{
> + uint16_t flags;
> +
> + if (weak_barriers) {
> +/* x86 prefers to using rte_smp_rmb over __atomic_load_n as it reports
> + * a better perf(~1.5%), which comes from the saved branch by the compiler.
> + * The if and else branch are identical with the smp and cio barriers
> +both
> + * defined as compiler barriers on x86.
> + */
> +#ifdef RTE_ARCH_X86_64
> + flags = dp->flags;
> + rte_smp_rmb();
> +#else
> + flags = __atomic_load_n(&dp->flags, __ATOMIC_ACQUIRE); #endif
> + } else {
> + flags = dp->flags;
> + rte_cio_rmb();
> + }
> +
> + return flags;
> +}
> +
> static inline void
> virtqueue_store_flags_packed(struct vring_packed_desc *dp,
> uint16_t flags, uint8_t weak_barriers) @@ -307,7 +333,7
> @@ desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq) {
> uint16_t used, avail, flags;
>
> - flags = desc->flags;
> + flags = virtqueue_fetch_flags_packed(desc, vq->hw->weak_barriers);
> used = !!(flags & VRING_PACKED_DESC_F_USED);
> avail = !!(flags & VRING_PACKED_DESC_F_AVAIL);
>
> diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index
> e7463ff..241d467 100644
> --- a/lib/librte_vhost/virtio_net.c
> +++ b/lib/librte_vhost/virtio_net.c
> @@ -110,8 +110,6 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
> used_idx -= vq->size;
> }
>
> - rte_smp_wmb();
> -
> for (i = 0; i < vq->shadow_used_idx; i++) {
> uint16_t flags;
>
> @@ -147,7 +145,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
> }
> }
>
> - vq->desc_packed[head_idx].flags = head_flags;
> + __atomic_store_n(&vq->desc_packed[head_idx].flags, head_flags,
> + __ATOMIC_RELEASE);
>
> vhost_log_cache_used_vring(dev, vq,
> head_idx *
> --
> 2.7.4
Hi Yinan,
Thanks for verification and reporting this, I will dump the assembly code and make an analysis after I am back from travel.
From my understanding the assembly code for x86 should be same, but I am not sure if anything we were missing.
Is this <1 perf drop coming from run to run variances, or system noise?
/Gavin
> -----Original Message-----
> From: Wang, Yinan <yinan.wang@intel.com>
> Sent: Wednesday, September 18, 2019 7:21 AM
> To: Joyce Kong (Arm Technology China) <Joyce.Kong@arm.com>;
> dev@dpdk.org
> Cc: nd <nd@arm.com>; maxime.coquelin@redhat.com; Richardson, Bruce
> <bruce.richardson@intel.com>; Bie, Tiwei <tiwei.bie@intel.com>; Wang,
> Zhihong <zhihong.wang@intel.com>; amorenoz@redhat.com; Wang, Xiao W
> <xiao.w.wang@intel.com>; Liu, Yong <yong.liu@intel.com>;
> jfreimann@redhat.com; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; Gavin Hu (Arm Technology China)
> <Gavin.Hu@arm.com>
> Subject: RE: [PATCH v4 2/2] virtio: one way barrier for packed vring desc used
> flags
>
>
> Hi Joyce,
>
> I test performance impact of your patch set with code base commit id:
> d03d8622db48918d14bfe805641b1766ecc40088, after applying your v4 patch
> set , packed ring shows small performance drop as below:
>
> PVP vhost/virtio 1c1q test commit:d03d8622db48918 apply v4
> patch set
>
> pvp_virtio11_mergeable 7.218 7.147
> pvp_virtio11_normal 7.217 7.182
>
>
> Thanks,
> Yinan
>
>
>
>
> > -----Original Message-----
> > From: Joyce Kong [mailto:joyce.kong@arm.com]
> > Sent: 2019年9月17日 13:28
> > To: dev@dpdk.org
> > Cc: nd@arm.com; maxime.coquelin@redhat.com; Wang, Yinan
> > <yinan.wang@intel.com>; Richardson, Bruce <bruce.richardson@intel.com>;
> Bie,
> > Tiwei <tiwei.bie@intel.com>; Wang, Zhihong <zhihong.wang@intel.com>;
> > amorenoz@redhat.com; Wang, Xiao W <xiao.w.wang@intel.com>; Liu, Yong
> > <yong.liu@intel.com>; jfreimann@redhat.com;
> honnappa.nagarahalli@arm.com;
> > gavin.hu@arm.com
> > Subject: [PATCH v4 2/2] virtio: one way barrier for packed vring desc used
> flags
> >
> > In case VIRTIO_F_ORDER_PLATFORM(36) is not negotiated, then the
> frontend
> > and backend are assumed to be implemented in software, that is they can
> run on
> > identical CPUs in an SMP configuration.
> > Thus a weak form of memory barriers like rte_smp_r/wmb, other than
> > rte_cio_r/wmb, is sufficient for this case(vq->hw->weak_barriers == 1) and
> > yields better performance.
> > For the above case, this patch helps yielding even better performance by
> > replacing the two-way barriers with C11 one-way barriers for used flags in
> packed
> > ring.
> >
> > Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> > Reviewed-by: Gavin Hu <gavin.hu@arm.com>
> > Reviewed-by: Phil Yang <phil.yang@arm.com>
> > Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> > ---
> > drivers/net/virtio/virtio_rxtx.c | 12 +++++++---
> > drivers/net/virtio/virtio_user/virtio_user_dev.c | 4 ++--
> > drivers/net/virtio/virtqueue.h | 28
> > +++++++++++++++++++++++-
> > lib/librte_vhost/virtio_net.c | 5 ++---
> > 4 files changed, 40 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> > index a87ffe1..2f0879c 100644
> > --- a/drivers/net/virtio/virtio_rxtx.c
> > +++ b/drivers/net/virtio/virtio_rxtx.c
> > @@ -122,9 +122,11 @@ virtqueue_dequeue_burst_rx_packed(struct
> virtqueue
> > *vq,
> >
> > for (i = 0; i < num; i++) {
> > used_idx = vq->vq_used_cons_idx;
> > + /* desc_is_used has a load-acquire or rte_cio_rmb inside
> > + * and wait for used desc in virtqueue.
> > + */
> > if (!desc_is_used(&desc[used_idx], vq))
> > return i;
> > - virtio_rmb(vq->hw->weak_barriers);
> > len[i] = desc[used_idx].len;
> > id = desc[used_idx].id;
> > cookie = (struct rte_mbuf *)vq->vq_descx[id].cookie; @@ -
> 233,8
> > +235,10 @@ virtio_xmit_cleanup_inorder_packed(struct virtqueue *vq, int
> num)
> > struct vq_desc_extra *dxp;
> >
> > used_idx = vq->vq_used_cons_idx;
> > + /* desc_is_used has a load-acquire or rte_cio_rmb inside
> > + * and wait for used desc in virtqueue.
> > + */
> > while (num > 0 && desc_is_used(&desc[used_idx], vq)) {
> > - virtio_rmb(vq->hw->weak_barriers);
> > id = desc[used_idx].id;
> > do {
> > curr_id = used_idx;
> > @@ -265,8 +269,10 @@ virtio_xmit_cleanup_normal_packed(struct
> virtqueue
> > *vq, int num)
> > struct vq_desc_extra *dxp;
> >
> > used_idx = vq->vq_used_cons_idx;
> > + /* desc_is_used has a load-acquire or rte_cio_rmb inside
> > + * and wait for used desc in virtqueue.
> > + */
> > while (num-- && desc_is_used(&desc[used_idx], vq)) {
> > - virtio_rmb(vq->hw->weak_barriers);
> > id = desc[used_idx].id;
> > dxp = &vq->vq_descx[id];
> > vq->vq_used_cons_idx += dxp->ndescs;
> > diff --git a/drivers/net/virtio/virtio_user/virtio_user_dev.c
> > b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> > index 7911c39..1c575d0 100644
> > --- a/drivers/net/virtio/virtio_user/virtio_user_dev.c
> > +++ b/drivers/net/virtio/virtio_user/virtio_user_dev.c
> > @@ -698,8 +698,8 @@ virtio_user_handle_cq_packed(struct
> virtio_user_dev
> > *dev, uint16_t queue_idx)
> > if (vq->used_wrap_counter)
> > flags |= VRING_PACKED_DESC_F_AVAIL_USED;
> >
> > - rte_smp_wmb();
> > - vring->desc[vq->used_idx].flags = flags;
> > + __atomic_store_n(&vring->desc[vq->used_idx].flags, flags,
> > + __ATOMIC_RELEASE);
> >
> > vq->used_idx += n_descs;
> > if (vq->used_idx >= dev->queue_size) { diff --git
> > a/drivers/net/virtio/virtqueue.h b/drivers/net/virtio/virtqueue.h index
> > b728ff8..8d7f197 100644
> > --- a/drivers/net/virtio/virtqueue.h
> > +++ b/drivers/net/virtio/virtqueue.h
> > @@ -54,6 +54,32 @@ virtio_wmb(uint8_t weak_barriers)
> > rte_cio_wmb();
> > }
> >
> > +static inline uint16_t
> > +virtqueue_fetch_flags_packed(struct vring_packed_desc *dp,
> > + uint8_t weak_barriers)
> > +{
> > + uint16_t flags;
> > +
> > + if (weak_barriers) {
> > +/* x86 prefers to using rte_smp_rmb over __atomic_load_n as it reports
> > + * a better perf(~1.5%), which comes from the saved branch by the
> compiler.
> > + * The if and else branch are identical with the smp and cio barriers
> > +both
> > + * defined as compiler barriers on x86.
> > + */
> > +#ifdef RTE_ARCH_X86_64
> > + flags = dp->flags;
> > + rte_smp_rmb();
> > +#else
> > + flags = __atomic_load_n(&dp->flags, __ATOMIC_ACQUIRE);
> #endif
> > + } else {
> > + flags = dp->flags;
> > + rte_cio_rmb();
> > + }
> > +
> > + return flags;
> > +}
> > +
> > static inline void
> > virtqueue_store_flags_packed(struct vring_packed_desc *dp,
> > uint16_t flags, uint8_t weak_barriers) @@ -307,7
> +333,7
> > @@ desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq) {
> > uint16_t used, avail, flags;
> >
> > - flags = desc->flags;
> > + flags = virtqueue_fetch_flags_packed(desc, vq->hw->weak_barriers);
> > used = !!(flags & VRING_PACKED_DESC_F_USED);
> > avail = !!(flags & VRING_PACKED_DESC_F_AVAIL);
> >
> > diff --git a/lib/librte_vhost/virtio_net.c b/lib/librte_vhost/virtio_net.c index
> > e7463ff..241d467 100644
> > --- a/lib/librte_vhost/virtio_net.c
> > +++ b/lib/librte_vhost/virtio_net.c
> > @@ -110,8 +110,6 @@ flush_shadow_used_ring_packed(struct virtio_net
> *dev,
> > used_idx -= vq->size;
> > }
> >
> > - rte_smp_wmb();
> > -
> > for (i = 0; i < vq->shadow_used_idx; i++) {
> > uint16_t flags;
> >
> > @@ -147,7 +145,8 @@ flush_shadow_used_ring_packed(struct virtio_net
> *dev,
> > }
> > }
> >
> > - vq->desc_packed[head_idx].flags = head_flags;
> > + __atomic_store_n(&vq->desc_packed[head_idx].flags, head_flags,
> > + __ATOMIC_RELEASE);
> >
> > vhost_log_cache_used_vring(dev, vq,
> > head_idx *
> > --
> > 2.7.4
On 9/17/19 7:28 AM, Joyce Kong wrote:
> In case VIRTIO_F_ORDER_PLATFORM(36) is not negotiated, then the frontend
> and backend are assumed to be implemented in software, that is they can
> run on identical CPUs in an SMP configuration.
> Thus a weak form of memory barriers like rte_smp_r/wmb, other than
> rte_cio_r/wmb, is sufficient for this case(vq->hw->weak_barriers == 1)
> and yields better performance.
> For the above case, this patch helps yielding even better performance
> by replacing the two-way barriers with C11 one-way barriers for used
> flags in packed ring.
>
> Signed-off-by: Joyce Kong <joyce.kong@arm.com>
> Reviewed-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Phil Yang <phil.yang@arm.com>
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
> drivers/net/virtio/virtio_rxtx.c | 12 +++++++---
> drivers/net/virtio/virtio_user/virtio_user_dev.c | 4 ++--
> drivers/net/virtio/virtqueue.h | 28 +++++++++++++++++++++++-
> lib/librte_vhost/virtio_net.c | 5 ++---
> 4 files changed, 40 insertions(+), 9 deletions(-)
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Thanks,
Maxime
@@ -122,9 +122,11 @@ virtqueue_dequeue_burst_rx_packed(struct virtqueue *vq,
for (i = 0; i < num; i++) {
used_idx = vq->vq_used_cons_idx;
+ /* desc_is_used has a load-acquire or rte_cio_rmb inside
+ * and wait for used desc in virtqueue.
+ */
if (!desc_is_used(&desc[used_idx], vq))
return i;
- virtio_rmb(vq->hw->weak_barriers);
len[i] = desc[used_idx].len;
id = desc[used_idx].id;
cookie = (struct rte_mbuf *)vq->vq_descx[id].cookie;
@@ -233,8 +235,10 @@ virtio_xmit_cleanup_inorder_packed(struct virtqueue *vq, int num)
struct vq_desc_extra *dxp;
used_idx = vq->vq_used_cons_idx;
+ /* desc_is_used has a load-acquire or rte_cio_rmb inside
+ * and wait for used desc in virtqueue.
+ */
while (num > 0 && desc_is_used(&desc[used_idx], vq)) {
- virtio_rmb(vq->hw->weak_barriers);
id = desc[used_idx].id;
do {
curr_id = used_idx;
@@ -265,8 +269,10 @@ virtio_xmit_cleanup_normal_packed(struct virtqueue *vq, int num)
struct vq_desc_extra *dxp;
used_idx = vq->vq_used_cons_idx;
+ /* desc_is_used has a load-acquire or rte_cio_rmb inside
+ * and wait for used desc in virtqueue.
+ */
while (num-- && desc_is_used(&desc[used_idx], vq)) {
- virtio_rmb(vq->hw->weak_barriers);
id = desc[used_idx].id;
dxp = &vq->vq_descx[id];
vq->vq_used_cons_idx += dxp->ndescs;
@@ -698,8 +698,8 @@ virtio_user_handle_cq_packed(struct virtio_user_dev *dev, uint16_t queue_idx)
if (vq->used_wrap_counter)
flags |= VRING_PACKED_DESC_F_AVAIL_USED;
- rte_smp_wmb();
- vring->desc[vq->used_idx].flags = flags;
+ __atomic_store_n(&vring->desc[vq->used_idx].flags, flags,
+ __ATOMIC_RELEASE);
vq->used_idx += n_descs;
if (vq->used_idx >= dev->queue_size) {
@@ -54,6 +54,32 @@ virtio_wmb(uint8_t weak_barriers)
rte_cio_wmb();
}
+static inline uint16_t
+virtqueue_fetch_flags_packed(struct vring_packed_desc *dp,
+ uint8_t weak_barriers)
+{
+ uint16_t flags;
+
+ if (weak_barriers) {
+/* x86 prefers to using rte_smp_rmb over __atomic_load_n as it reports
+ * a better perf(~1.5%), which comes from the saved branch by the compiler.
+ * The if and else branch are identical with the smp and cio barriers both
+ * defined as compiler barriers on x86.
+ */
+#ifdef RTE_ARCH_X86_64
+ flags = dp->flags;
+ rte_smp_rmb();
+#else
+ flags = __atomic_load_n(&dp->flags, __ATOMIC_ACQUIRE);
+#endif
+ } else {
+ flags = dp->flags;
+ rte_cio_rmb();
+ }
+
+ return flags;
+}
+
static inline void
virtqueue_store_flags_packed(struct vring_packed_desc *dp,
uint16_t flags, uint8_t weak_barriers)
@@ -307,7 +333,7 @@ desc_is_used(struct vring_packed_desc *desc, struct virtqueue *vq)
{
uint16_t used, avail, flags;
- flags = desc->flags;
+ flags = virtqueue_fetch_flags_packed(desc, vq->hw->weak_barriers);
used = !!(flags & VRING_PACKED_DESC_F_USED);
avail = !!(flags & VRING_PACKED_DESC_F_AVAIL);
@@ -110,8 +110,6 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
used_idx -= vq->size;
}
- rte_smp_wmb();
-
for (i = 0; i < vq->shadow_used_idx; i++) {
uint16_t flags;
@@ -147,7 +145,8 @@ flush_shadow_used_ring_packed(struct virtio_net *dev,
}
}
- vq->desc_packed[head_idx].flags = head_flags;
+ __atomic_store_n(&vq->desc_packed[head_idx].flags, head_flags,
+ __ATOMIC_RELEASE);
vhost_log_cache_used_vring(dev, vq,
head_idx *