[PATCH v3] vhost: add IRQ suppression

[PATCH v3] vhost: add IRQ suppression

[Maxime Coquelin]

Guest notifications offloading, which has been introduced
in v23.07, aims at offloading syscalls out of the datapath.

This patch optimizes the offloading by not offloading the
guest notification for a given virtqueue if one is already
being offloaded by the application.

With a single VDUSE device, we can already see few
notifications being suppressed when doing throughput
testing with Iperf3. We can expect to see much more being
suppressed when the offloading thread is under pressure.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---

v3: s/0/false/ (David)

 lib/vhost/vhost.c |  4 ++++
 lib/vhost/vhost.h | 27 +++++++++++++++++++++------
 2 files changed, 25 insertions(+), 6 deletions(-)

diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index c03bb9c6eb..7fde412ef3 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -49,6 +49,8 @@ static const struct vhost_vq_stats_name_off vhost_vq_stat_strings[] = {
 		stats.guest_notifications_offloaded)},
 	{"guest_notifications_error", offsetof(struct vhost_virtqueue,
 		stats.guest_notifications_error)},
+	{"guest_notifications_suppressed", offsetof(struct vhost_virtqueue,
+		stats.guest_notifications_suppressed)},
 	{"iotlb_hits",             offsetof(struct vhost_virtqueue, stats.iotlb_hits)},
 	{"iotlb_misses",           offsetof(struct vhost_virtqueue, stats.iotlb_misses)},
 	{"inflight_submitted",     offsetof(struct vhost_virtqueue, stats.inflight_submitted)},
@@ -1517,6 +1519,8 @@ rte_vhost_notify_guest(int vid, uint16_t queue_id)

 	rte_rwlock_read_lock(&vq->access_lock);

+	__atomic_store_n(&vq->irq_pending, false, __ATOMIC_RELEASE);
+
 	if (dev->backend_ops->inject_irq(dev, vq)) {
 		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
 			__atomic_fetch_add(&vq->stats.guest_notifications_error,
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index 9723429b1c..5fc9035a1f 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -156,6 +156,7 @@ struct virtqueue_stats {
 	uint64_t iotlb_misses;
 	uint64_t inflight_submitted;
 	uint64_t inflight_completed;
+	uint64_t guest_notifications_suppressed;
 	/* Counters below are atomic, and should be incremented as such. */
 	uint64_t guest_notifications;
 	uint64_t guest_notifications_offloaded;
@@ -346,6 +347,8 @@ struct vhost_virtqueue {

 	struct vhost_vring_addr ring_addrs;
 	struct virtqueue_stats	stats;
+
+	bool irq_pending;
 } __rte_cache_aligned;

 /* Virtio device status as per Virtio specification */
@@ -908,12 +911,24 @@ vhost_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
 static __rte_always_inline void
 vhost_vring_inject_irq(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
-	if (dev->notify_ops->guest_notify &&
-	    dev->notify_ops->guest_notify(dev->vid, vq->index)) {
-		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
-			__atomic_fetch_add(&vq->stats.guest_notifications_offloaded,
-				1, __ATOMIC_RELAXED);
-		return;
+	bool expected = false;
+
+	if (dev->notify_ops->guest_notify) {
+		if (__atomic_compare_exchange_n(&vq->irq_pending, &expected, true, 0,
+				  __ATOMIC_RELEASE, __ATOMIC_RELAXED)) {
+			if (dev->notify_ops->guest_notify(dev->vid, vq->index)) {
+				if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
+					__atomic_fetch_add(&vq->stats.guest_notifications_offloaded,
+						1, __ATOMIC_RELAXED);
+				return;
+			}
+
+			/* Offloading failed, fallback to direct IRQ injection */
+			__atomic_store_n(&vq->irq_pending, false, __ATOMIC_RELEASE);
+		} else {
+			vq->stats.guest_notifications_suppressed++;
+			return;
+		}
 	}

 	if (dev->backend_ops->inject_irq(dev, vq)) {
--
2.41.0

Re: [PATCH v3] vhost: add IRQ suppression

[Eelco Chaudron]

On 29 Sep 2023, at 12:38, Maxime Coquelin wrote:

> Guest notifications offloading, which has been introduced
> in v23.07, aims at offloading syscalls out of the datapath.
>
> This patch optimizes the offloading by not offloading the
> guest notification for a given virtqueue if one is already
> being offloaded by the application.
>
> With a single VDUSE device, we can already see few
> notifications being suppressed when doing throughput
> testing with Iperf3. We can expect to see much more being
> suppressed when the offloading thread is under pressure.
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks for adding this Maxime. I did some tests with OVS and my old determinism patchset, and it works perfectly.

I have two small nits, but this change looks good to me.

Acked-by: Eelco Chaudron <echaudro@redhat.com>

> ---
>
> v3: s/0/false/ (David)
>
>  lib/vhost/vhost.c |  4 ++++
>  lib/vhost/vhost.h | 27 +++++++++++++++++++++------
>  2 files changed, 25 insertions(+), 6 deletions(-)
>
> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
> index c03bb9c6eb..7fde412ef3 100644
> --- a/lib/vhost/vhost.c
> +++ b/lib/vhost/vhost.c
> @@ -49,6 +49,8 @@ static const struct vhost_vq_stats_name_off vhost_vq_stat_strings[] = {
>  		stats.guest_notifications_offloaded)},
>  	{"guest_notifications_error", offsetof(struct vhost_virtqueue,
>  		stats.guest_notifications_error)},
> +	{"guest_notifications_suppressed", offsetof(struct vhost_virtqueue,
> +		stats.guest_notifications_suppressed)},
>  	{"iotlb_hits",             offsetof(struct vhost_virtqueue, stats.iotlb_hits)},
>  	{"iotlb_misses",           offsetof(struct vhost_virtqueue, stats.iotlb_misses)},
>  	{"inflight_submitted",     offsetof(struct vhost_virtqueue, stats.inflight_submitted)},
> @@ -1517,6 +1519,8 @@ rte_vhost_notify_guest(int vid, uint16_t queue_id)
>
>  	rte_rwlock_read_lock(&vq->access_lock);
>
> +	__atomic_store_n(&vq->irq_pending, false, __ATOMIC_RELEASE);
> +
>  	if (dev->backend_ops->inject_irq(dev, vq)) {
>  		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
>  			__atomic_fetch_add(&vq->stats.guest_notifications_error,
> diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
> index 9723429b1c..5fc9035a1f 100644
> --- a/lib/vhost/vhost.h
> +++ b/lib/vhost/vhost.h
> @@ -156,6 +156,7 @@ struct virtqueue_stats {
>  	uint64_t iotlb_misses;
>  	uint64_t inflight_submitted;
>  	uint64_t inflight_completed;
> +	uint64_t guest_notifications_suppressed;
>  	/* Counters below are atomic, and should be incremented as such. */
>  	uint64_t guest_notifications;
>  	uint64_t guest_notifications_offloaded;
> @@ -346,6 +347,8 @@ struct vhost_virtqueue {
>
>  	struct vhost_vring_addr ring_addrs;
>  	struct virtqueue_stats	stats;
> +
> +	bool irq_pending;

nit: Other elements in this structure have the names aligned, not sure if this should be done for this item also.

>  } __rte_cache_aligned;
>
>  /* Virtio device status as per Virtio specification */
> @@ -908,12 +911,24 @@ vhost_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
>  static __rte_always_inline void
>  vhost_vring_inject_irq(struct virtio_net *dev, struct vhost_virtqueue *vq)
>  {
> -	if (dev->notify_ops->guest_notify &&
> -	    dev->notify_ops->guest_notify(dev->vid, vq->index)) {
> -		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
> -			__atomic_fetch_add(&vq->stats.guest_notifications_offloaded,
> -				1, __ATOMIC_RELAXED);
> -		return;
> +	bool expected = false;
> +
> +	if (dev->notify_ops->guest_notify) {
> +		if (__atomic_compare_exchange_n(&vq->irq_pending, &expected, true, 0,
> +				  __ATOMIC_RELEASE, __ATOMIC_RELAXED)) {
> +			if (dev->notify_ops->guest_notify(dev->vid, vq->index)) {
> +				if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
> +					__atomic_fetch_add(&vq->stats.guest_notifications_offloaded,
> +						1, __ATOMIC_RELAXED);
> +				return;
> +			}
> +
> +			/* Offloading failed, fallback to direct IRQ injection */

nit: Some comments end with a dot and some do not, not sure what is the preference in DPDK.

> +			__atomic_store_n(&vq->irq_pending, false, __ATOMIC_RELEASE);
> +		} else {
> +			vq->stats.guest_notifications_suppressed++;
> +			return;
> +		}
>  	}
>
>  	if (dev->backend_ops->inject_irq(dev, vq)) {
> --
> 2.41.0

Re: [PATCH v3] vhost: add IRQ suppression

[Maxime Coquelin]

Hi Eelco,

On 10/3/23 14:36, Eelco Chaudron wrote:
> 
> 
> On 29 Sep 2023, at 12:38, Maxime Coquelin wrote:
> 
>> Guest notifications offloading, which has been introduced
>> in v23.07, aims at offloading syscalls out of the datapath.
>>
>> This patch optimizes the offloading by not offloading the
>> guest notification for a given virtqueue if one is already
>> being offloaded by the application.
>>
>> With a single VDUSE device, we can already see few
>> notifications being suppressed when doing throughput
>> testing with Iperf3. We can expect to see much more being
>> suppressed when the offloading thread is under pressure.
>>
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> 
> Thanks for adding this Maxime. I did some tests with OVS and my old determinism patchset, and it works perfectly.
> 
> I have two small nits, but this change looks good to me.
> 
> Acked-by: Eelco Chaudron <echaudro@redhat.com>
> 
>> ---
>>
>> v3: s/0/false/ (David)
>>
>>   lib/vhost/vhost.c |  4 ++++
>>   lib/vhost/vhost.h | 27 +++++++++++++++++++++------
>>   2 files changed, 25 insertions(+), 6 deletions(-)
>>
>> diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
>> index c03bb9c6eb..7fde412ef3 100644
>> --- a/lib/vhost/vhost.c
>> +++ b/lib/vhost/vhost.c
>> @@ -49,6 +49,8 @@ static const struct vhost_vq_stats_name_off vhost_vq_stat_strings[] = {
>>   		stats.guest_notifications_offloaded)},
>>   	{"guest_notifications_error", offsetof(struct vhost_virtqueue,
>>   		stats.guest_notifications_error)},
>> +	{"guest_notifications_suppressed", offsetof(struct vhost_virtqueue,
>> +		stats.guest_notifications_suppressed)},
>>   	{"iotlb_hits",             offsetof(struct vhost_virtqueue, stats.iotlb_hits)},
>>   	{"iotlb_misses",           offsetof(struct vhost_virtqueue, stats.iotlb_misses)},
>>   	{"inflight_submitted",     offsetof(struct vhost_virtqueue, stats.inflight_submitted)},
>> @@ -1517,6 +1519,8 @@ rte_vhost_notify_guest(int vid, uint16_t queue_id)
>>
>>   	rte_rwlock_read_lock(&vq->access_lock);
>>
>> +	__atomic_store_n(&vq->irq_pending, false, __ATOMIC_RELEASE);
>> +
>>   	if (dev->backend_ops->inject_irq(dev, vq)) {
>>   		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
>>   			__atomic_fetch_add(&vq->stats.guest_notifications_error,
>> diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
>> index 9723429b1c..5fc9035a1f 100644
>> --- a/lib/vhost/vhost.h
>> +++ b/lib/vhost/vhost.h
>> @@ -156,6 +156,7 @@ struct virtqueue_stats {
>>   	uint64_t iotlb_misses;
>>   	uint64_t inflight_submitted;
>>   	uint64_t inflight_completed;
>> +	uint64_t guest_notifications_suppressed;
>>   	/* Counters below are atomic, and should be incremented as such. */
>>   	uint64_t guest_notifications;
>>   	uint64_t guest_notifications_offloaded;
>> @@ -346,6 +347,8 @@ struct vhost_virtqueue {
>>
>>   	struct vhost_vring_addr ring_addrs;
>>   	struct virtqueue_stats	stats;
>> +
>> +	bool irq_pending;
> 
> nit: Other elements in this structure have the names aligned, not sure if this should be done for this item also.

Ha yes, you're right.
I'll fix it while applying.

> 
>>   } __rte_cache_aligned;
>>
>>   /* Virtio device status as per Virtio specification */
>> @@ -908,12 +911,24 @@ vhost_need_event(uint16_t event_idx, uint16_t new_idx, uint16_t old)
>>   static __rte_always_inline void
>>   vhost_vring_inject_irq(struct virtio_net *dev, struct vhost_virtqueue *vq)
>>   {
>> -	if (dev->notify_ops->guest_notify &&
>> -	    dev->notify_ops->guest_notify(dev->vid, vq->index)) {
>> -		if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
>> -			__atomic_fetch_add(&vq->stats.guest_notifications_offloaded,
>> -				1, __ATOMIC_RELAXED);
>> -		return;
>> +	bool expected = false;
>> +
>> +	if (dev->notify_ops->guest_notify) {
>> +		if (__atomic_compare_exchange_n(&vq->irq_pending, &expected, true, 0,
>> +				  __ATOMIC_RELEASE, __ATOMIC_RELAXED)) {
>> +			if (dev->notify_ops->guest_notify(dev->vid, vq->index)) {
>> +				if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
>> +					__atomic_fetch_add(&vq->stats.guest_notifications_offloaded,
>> +						1, __ATOMIC_RELAXED);
>> +				return;
>> +			}
>> +
>> +			/* Offloading failed, fallback to direct IRQ injection */
> 
> nit: Some comments end with a dot and some do not, not sure what is the preference in DPDK.

I'm not sure either! I'm personally fine either way.

>> +			__atomic_store_n(&vq->irq_pending, false, __ATOMIC_RELEASE);
>> +		} else {
>> +			vq->stats.guest_notifications_suppressed++;
>> +			return;
>> +		}
>>   	}
>>
>>   	if (dev->backend_ops->inject_irq(dev, vq)) {
>> --
>> 2.41.0
> 

Thanks,
Maxime

Re: [PATCH v3] vhost: add IRQ suppression

[David Marchand]

On Fri, Sep 29, 2023 at 12:38 PM Maxime Coquelin
<maxime.coquelin@redhat.com> wrote:
>
> Guest notifications offloading, which has been introduced
> in v23.07, aims at offloading syscalls out of the datapath.
>
> This patch optimizes the offloading by not offloading the
> guest notification for a given virtqueue if one is already
> being offloaded by the application.
>
> With a single VDUSE device, we can already see few
> notifications being suppressed when doing throughput
> testing with Iperf3. We can expect to see much more being
> suppressed when the offloading thread is under pressure.
>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>

This looks like a good idea.
Reviewed-by: David Marchand <david.marchand@redhat.com>


-- 
David Marchand

Re: [PATCH v3] vhost: add IRQ suppression

[Maxime Coquelin]

On 9/29/23 12:38, Maxime Coquelin wrote:
> Guest notifications offloading, which has been introduced
> in v23.07, aims at offloading syscalls out of the datapath.
> 
> This patch optimizes the offloading by not offloading the
> guest notification for a given virtqueue if one is already
> being offloaded by the application.
> 
> With a single VDUSE device, we can already see few
> notifications being suppressed when doing throughput
> testing with Iperf3. We can expect to see much more being
> suppressed when the offloading thread is under pressure.
> 
> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
> 
> v3: s/0/false/ (David)
> 
>   lib/vhost/vhost.c |  4 ++++
>   lib/vhost/vhost.h | 27 +++++++++++++++++++++------
>   2 files changed, 25 insertions(+), 6 deletions(-)
> 
Applied to nex-virtio/for-next-net.

Thanks,
Maxime