[PATCH v2 net 0/3] sfc: ARFS fixes

[PATCH v2 net 0/3] sfc: ARFS fixes

[Edward Cree]

Three issues introduced by my recent asynchronous filter handling changes:
1. The old filter_rfs_insert would replace a matching filter of equal
   priority; we need to pass the appropriate argument to filter_insert to
   make it do the same.
2. We're lying to the kernel with our return value from ndo_rx_flow_steer,
   so we need to lie consistently when calling rps_may_expire_flow.  This
   is only a partial fix, as the lie still prevents us from steering
   multiple flows with the same ID to different queues; a proper fix that
   stops us lying at all will hopefully follow later.
3. It's possible to cause the kernel to hammer ndo_rx_flow_steer very
   hard, so make sure we don't build up too huge a backlog of workitems.

Possibly it would be better to fix #3 on the kernel side; I have a patch
 which I think does that but it's not a regression in 4.17 so isn't 'net'
 material.
There's also the issue that we come up in the bad configuration that
 triggers #3 by default, but that too is a problem for another time.

Edward Cree (3):
  sfc: insert ARFS filters with replace_equal=true
  sfc: pass the correctly bogus filter_id to rps_may_expire_flow()
  sfc: limit ARFS workitems in flight per channel

 drivers/net/ethernet/sfc/ef10.c       |  3 +-
 drivers/net/ethernet/sfc/farch.c      |  2 +-
 drivers/net/ethernet/sfc/net_driver.h | 25 +++++++++++++++
 drivers/net/ethernet/sfc/rx.c         | 60 ++++++++++++++++++-----------------
 4 files changed, 58 insertions(+), 32 deletions(-)

[PATCH v2 net 1/3] sfc: insert ARFS filters with replace_equal=true

[Edward Cree]

Necessary to allow redirecting a flow when the application moves.

Fixes: 3af0f34290f6 ("sfc: replace asynchronous filter operations")
Signed-off-by: Edward Cree <ecree@solarflare.com>
---
 drivers/net/ethernet/sfc/rx.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 95682831484e..13b0eb71dbf3 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -851,7 +851,7 @@ static void efx_filter_rfs_work(struct work_struct *data)
 	struct efx_channel *channel = efx_get_channel(efx, req->rxq_index);
 	int rc;
 
-	rc = efx->type->filter_insert(efx, &req->spec, false);
+	rc = efx->type->filter_insert(efx, &req->spec, true);
 	if (rc >= 0) {
 		/* Remember this so we can check whether to expire the filter
 		 * later.

[PATCH v2 net 2/3] sfc: pass the correctly bogus filter_id to rps_may_expire_flow()

[Edward Cree]

When we inserted an ARFS filter for ndo_rx_flow_steer(), we didn't know
 what the filter ID would be, so we just returned 0.  Thus, we must also
 pass 0 as the filter ID when calling rps_may_expire_flow() for it, and
 rely on the flow_id to identify what we're talking about.

Fixes: 3af0f34290f6 ("sfc: replace asynchronous filter operations")
Signed-off-by: Edward Cree <ecree@solarflare.com>
---
 drivers/net/ethernet/sfc/ef10.c  | 3 +--
 drivers/net/ethernet/sfc/farch.c | 2 +-
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/sfc/ef10.c b/drivers/net/ethernet/sfc/ef10.c
index 50daad0a1482..36f24c7e553a 100644
--- a/drivers/net/ethernet/sfc/ef10.c
+++ b/drivers/net/ethernet/sfc/ef10.c
@@ -4776,8 +4776,7 @@ static bool efx_ef10_filter_rfs_expire_one(struct efx_nic *efx, u32 flow_id,
 		goto out_unlock;
 	}
 
-	if (!rps_may_expire_flow(efx->net_dev, spec->dmaq_id,
-				 flow_id, filter_idx)) {
+	if (!rps_may_expire_flow(efx->net_dev, spec->dmaq_id, flow_id, 0)) {
 		ret = false;
 		goto out_unlock;
 	}
diff --git a/drivers/net/ethernet/sfc/farch.c b/drivers/net/ethernet/sfc/farch.c
index 4a19c7efdf8d..7174ef5e5c5e 100644
--- a/drivers/net/ethernet/sfc/farch.c
+++ b/drivers/net/ethernet/sfc/farch.c
@@ -2912,7 +2912,7 @@ bool efx_farch_filter_rfs_expire_one(struct efx_nic *efx, u32 flow_id,
 	if (test_bit(index, table->used_bitmap) &&
 	    table->spec[index].priority == EFX_FILTER_PRI_HINT &&
 	    rps_may_expire_flow(efx->net_dev, table->spec[index].dmaq_id,
-				flow_id, index)) {
+				flow_id, 0)) {
 		efx_farch_filter_table_clear_entry(efx, table, index);
 		ret = true;
 	}

[PATCH v2 net 3/3] sfc: limit ARFS workitems in flight per channel

[Edward Cree]

A misconfigured system (e.g. with all interrupts affinitised to all CPUs)
 may produce a storm of ARFS steering events.  With the existing sfc ARFS
 implementation, that could create a backlog of workitems that grinds the
 system to a halt.  To prevent this, limit the number of workitems that
 may be in flight for a given SFC device to 8 (EFX_RPS_MAX_IN_FLIGHT), and
 return EBUSY from our ndo_rx_flow_steer method if the limit is reached.
Given this limit, also store the workitems in an array of slots within the
 struct efx_nic, rather than dynamically allocating for each request.
The limit should not negatively impact performance, because it is only
 likely to be hit in cases where ARFS will be ineffective anyway.

Signed-off-by: Edward Cree <ecree@solarflare.com>
---
 drivers/net/ethernet/sfc/net_driver.h | 25 +++++++++++++++
 drivers/net/ethernet/sfc/rx.c         | 58 ++++++++++++++++++-----------------
 2 files changed, 55 insertions(+), 28 deletions(-)

diff --git a/drivers/net/ethernet/sfc/net_driver.h b/drivers/net/ethernet/sfc/net_driver.h
index 5e379a83c729..eea3808b3f25 100644
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -733,6 +733,27 @@ struct efx_rss_context {
 	u32 rx_indir_table[128];
 };
 
+#ifdef CONFIG_RFS_ACCEL
+/**
+ * struct efx_async_filter_insertion - Request to asynchronously insert a filter
+ * @net_dev: Reference to the netdevice
+ * @spec: The filter to insert
+ * @work: Workitem for this request
+ * @rxq_index: Identifies the channel for which this request was made
+ * @flow_id: Identifies the kernel-side flow for which this request was made
+ */
+struct efx_async_filter_insertion {
+	struct net_device *net_dev;
+	struct efx_filter_spec spec;
+	struct work_struct work;
+	u16 rxq_index;
+	u32 flow_id;
+};
+
+/* Maximum number of ARFS workitems that may be in flight on an efx_nic */
+#define EFX_RPS_MAX_IN_FLIGHT	8
+#endif /* CONFIG_RFS_ACCEL */
+
 /**
  * struct efx_nic - an Efx NIC
  * @name: Device name (net device name or bus id before net device registered)
@@ -850,6 +871,8 @@ struct efx_rss_context {
  * @rps_expire_channel: Next channel to check for expiry
  * @rps_expire_index: Next index to check for expiry in
  *	@rps_expire_channel's @rps_flow_id
+ * @rps_slot_map: bitmap of in-flight entries in @rps_slot
+ * @rps_slot: array of ARFS insertion requests for efx_filter_rfs_work()
  * @active_queues: Count of RX and TX queues that haven't been flushed and drained.
  * @rxq_flush_pending: Count of number of receive queues that need to be flushed.
  *	Decremented when the efx_flush_rx_queue() is called.
@@ -1004,6 +1027,8 @@ struct efx_nic {
 	struct mutex rps_mutex;
 	unsigned int rps_expire_channel;
 	unsigned int rps_expire_index;
+	unsigned long rps_slot_map;
+	struct efx_async_filter_insertion rps_slot[EFX_RPS_MAX_IN_FLIGHT];
 #endif
 
 	atomic_t active_queues;
diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index 13b0eb71dbf3..9c593c661cbf 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -827,28 +827,13 @@ MODULE_PARM_DESC(rx_refill_threshold,
 
 #ifdef CONFIG_RFS_ACCEL
 
-/**
- * struct efx_async_filter_insertion - Request to asynchronously insert a filter
- * @net_dev: Reference to the netdevice
- * @spec: The filter to insert
- * @work: Workitem for this request
- * @rxq_index: Identifies the channel for which this request was made
- * @flow_id: Identifies the kernel-side flow for which this request was made
- */
-struct efx_async_filter_insertion {
-	struct net_device *net_dev;
-	struct efx_filter_spec spec;
-	struct work_struct work;
-	u16 rxq_index;
-	u32 flow_id;
-};
-
 static void efx_filter_rfs_work(struct work_struct *data)
 {
 	struct efx_async_filter_insertion *req = container_of(data, struct efx_async_filter_insertion,
 							      work);
 	struct efx_nic *efx = netdev_priv(req->net_dev);
 	struct efx_channel *channel = efx_get_channel(efx, req->rxq_index);
+	int slot_idx = req - efx->rps_slot;
 	int rc;
 
 	rc = efx->type->filter_insert(efx, &req->spec, true);
@@ -878,8 +863,8 @@ static void efx_filter_rfs_work(struct work_struct *data)
 	}
 
 	/* Release references */
+	clear_bit(slot_idx, &efx->rps_slot_map);
 	dev_put(req->net_dev);
-	kfree(req);
 }
 
 int efx_filter_rfs(struct net_device *net_dev, const struct sk_buff *skb,
@@ -888,22 +873,36 @@ int efx_filter_rfs(struct net_device *net_dev, const struct sk_buff *skb,
 	struct efx_nic *efx = netdev_priv(net_dev);
 	struct efx_async_filter_insertion *req;
 	struct flow_keys fk;
+	int slot_idx;
+	int rc;
 
-	if (flow_id == RPS_FLOW_ID_INVALID)
-		return -EINVAL;
+	/* find a free slot */
+	for (slot_idx = 0; slot_idx < EFX_RPS_MAX_IN_FLIGHT; slot_idx++)
+		if (!test_and_set_bit(slot_idx, &efx->rps_slot_map))
+			break;
+	if (slot_idx >= EFX_RPS_MAX_IN_FLIGHT)
+		return -EBUSY;
 
-	if (!skb_flow_dissect_flow_keys(skb, &fk, 0))
-		return -EPROTONOSUPPORT;
+	if (flow_id == RPS_FLOW_ID_INVALID) {
+		rc = -EINVAL;
+		goto out_clear;
+	}
 
-	if (fk.basic.n_proto != htons(ETH_P_IP) && fk.basic.n_proto != htons(ETH_P_IPV6))
-		return -EPROTONOSUPPORT;
-	if (fk.control.flags & FLOW_DIS_IS_FRAGMENT)
-		return -EPROTONOSUPPORT;
+	if (!skb_flow_dissect_flow_keys(skb, &fk, 0)) {
+		rc = -EPROTONOSUPPORT;
+		goto out_clear;
+	}
 
-	req = kmalloc(sizeof(*req), GFP_ATOMIC);
-	if (!req)
-		return -ENOMEM;
+	if (fk.basic.n_proto != htons(ETH_P_IP) && fk.basic.n_proto != htons(ETH_P_IPV6)) {
+		rc = -EPROTONOSUPPORT;
+		goto out_clear;
+	}
+	if (fk.control.flags & FLOW_DIS_IS_FRAGMENT) {
+		rc = -EPROTONOSUPPORT;
+		goto out_clear;
+	}
 
+	req = efx->rps_slot + slot_idx;
 	efx_filter_init_rx(&req->spec, EFX_FILTER_PRI_HINT,
 			   efx->rx_scatter ? EFX_FILTER_FLAG_RX_SCATTER : 0,
 			   rxq_index);
@@ -933,6 +932,9 @@ int efx_filter_rfs(struct net_device *net_dev, const struct sk_buff *skb,
 	req->flow_id = flow_id;
 	schedule_work(&req->work);
 	return 0;
+out_clear:
+	clear_bit(slot_idx, &efx->rps_slot_map);
+	return rc;
 }
 
 bool __efx_filter_rfs_expire(struct efx_nic *efx, unsigned int quota)

Re: [PATCH v2 net 0/3] sfc: ARFS fixes

[David Miller]

From: Edward Cree <ecree@solarflare.com>
Date: Fri, 13 Apr 2018 19:16:20 +0100

> Three issues introduced by my recent asynchronous filter handling changes:
> 1. The old filter_rfs_insert would replace a matching filter of equal
>    priority; we need to pass the appropriate argument to filter_insert to
>    make it do the same.
> 2. We're lying to the kernel with our return value from ndo_rx_flow_steer,
>    so we need to lie consistently when calling rps_may_expire_flow.  This
>    is only a partial fix, as the lie still prevents us from steering
>    multiple flows with the same ID to different queues; a proper fix that
>    stops us lying at all will hopefully follow later.
> 3. It's possible to cause the kernel to hammer ndo_rx_flow_steer very
>    hard, so make sure we don't build up too huge a backlog of workitems.
> 
> Possibly it would be better to fix #3 on the kernel side; I have a patch
>  which I think does that but it's not a regression in 4.17 so isn't 'net'
>  material.
> There's also the issue that we come up in the bad configuration that
>  triggers #3 by default, but that too is a problem for another time.

Series applied, thanks Edward.