[PATCH net-next 0/2] net: add netif_set_real_num_queues() for device reconfig

[PATCH net-next 0/2] net: add netif_set_real_num_queues() for device reconfig

[Jakub Kicinski]

This short set adds a helper to make the implementation of
two-phase NIC reconfig easier.

Jakub Kicinski (2):
  net: add netif_set_real_num_queues() for device reconfig
  nfp: use netif_set_real_num_queues()

 .../ethernet/netronome/nfp/nfp_net_common.c   | 11 ++---
 include/linux/netdevice.h                     |  2 +
 net/core/dev.c                                | 44 +++++++++++++++++++
 3 files changed, 49 insertions(+), 8 deletions(-)

-- 
2.31.1

[PATCH net-next 1/2] net: add netif_set_real_num_queues() for device reconfig

[Jakub Kicinski]

netif_set_real_num_rx_queues() and netif_set_real_num_tx_queues()
can fail which breaks drivers trying to implement reconfiguration
in a way that can't leave the device half-broken. In other words
those functions are incompatible with prepare/commit approach.

Luckily setting real number of queues can fail only if the number
is increased, meaning that if we order operations correctly we
can guarantee ending up with either new config (success), or
the old one (on error).

Provide a helper implementing such logic so that drivers don't
have to duplicate it.

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 include/linux/netdevice.h |  2 ++
 net/core/dev.c            | 44 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cd136499ec59..1b4d4509d04b 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3916,6 +3916,8 @@ static inline int netif_set_real_num_rx_queues(struct net_device *dev,
 	return 0;
 }
 #endif
+int netif_set_real_num_queues(struct net_device *dev,
+			      unsigned int txq, unsigned int rxq);
 
 static inline struct netdev_rx_queue *
 __netif_get_rx_queue(struct net_device *dev, unsigned int rxq)
diff --git a/net/core/dev.c b/net/core/dev.c
index 4a1401008db9..360cb2f1b1e9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2973,6 +2973,50 @@ int netif_set_real_num_rx_queues(struct net_device *dev, unsigned int rxq)
 EXPORT_SYMBOL(netif_set_real_num_rx_queues);
 #endif
 
+/**
+ *	netif_set_real_num_queues - set actual number of RX and TX queues used
+ *	@dev: Network device
+ *	@txq: Actual number of TX queues
+ *	@rxq: Actual number of RX queues
+ *
+ *	Set the real number of both TX and RX queues.
+ *	Does nothing if the number of queues is already correct.
+ */
+int netif_set_real_num_queues(struct net_device *dev,
+			      unsigned int txq, unsigned int rxq)
+{
+	unsigned int old_rxq = dev->real_num_rx_queues;
+	int err;
+
+	if (txq < 1 || txq > dev->num_tx_queues ||
+	    rxq < 1 || rxq > dev->num_rx_queues)
+		return -EINVAL;
+
+	/* Start from increases, so the error path only does decreases -
+	 * decreases can't fail.
+	 */
+	if (rxq > dev->real_num_rx_queues) {
+		err = netif_set_real_num_rx_queues(dev, rxq);
+		if (err)
+			return err;
+	}
+	if (txq > dev->real_num_tx_queues) {
+		err = netif_set_real_num_tx_queues(dev, txq);
+		if (err)
+			goto undo_rx;
+	}
+	if (rxq < dev->real_num_rx_queues)
+		WARN_ON(netif_set_real_num_rx_queues(dev, rxq));
+	if (txq < dev->real_num_tx_queues)
+		WARN_ON(netif_set_real_num_tx_queues(dev, txq));
+
+	return 0;
+undo_rx:
+	WARN_ON(netif_set_real_num_rx_queues(dev, old_rxq));
+	return err;
+}
+EXPORT_SYMBOL(netif_set_real_num_queues);
+
 /**
  * netif_get_num_default_rss_queues - default number of RSS queues
  *
-- 
2.31.1

[PATCH net-next 2/2] nfp: use netif_set_real_num_queues()

[Jakub Kicinski]

Avoid reconfig problems due to failures in netif_set_real_num_tx_queues()
by using netif_set_real_num_queues().

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 drivers/net/ethernet/netronome/nfp/nfp_net_common.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
index 15078f9dc9f1..5bfa22accf2c 100644
--- a/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
+++ b/drivers/net/ethernet/netronome/nfp/nfp_net_common.c
@@ -3281,17 +3281,12 @@ static int nfp_net_dp_swap_enable(struct nfp_net *nn, struct nfp_net_dp *dp)
 	for (r = 0; r <	nn->max_r_vecs; r++)
 		nfp_net_vector_assign_rings(&nn->dp, &nn->r_vecs[r], r);
 
-	err = netif_set_real_num_rx_queues(nn->dp.netdev, nn->dp.num_rx_rings);
+	err = netif_set_real_num_queues(nn->dp.netdev,
+					nn->dp.num_stack_tx_rings,
+					nn->dp.num_rx_rings);
 	if (err)
 		return err;
 
-	if (nn->dp.netdev->real_num_tx_queues != nn->dp.num_stack_tx_rings) {
-		err = netif_set_real_num_tx_queues(nn->dp.netdev,
-						   nn->dp.num_stack_tx_rings);
-		if (err)
-			return err;
-	}
-
 	return nfp_net_set_config_and_enable(nn);
 }
 
-- 
2.31.1

Re: [PATCH net-next 0/2] net: add netif_set_real_num_queues() for device reconfig

[Simon Horman]

On Tue, Aug 03, 2021 at 06:05:25AM -0700, Jakub Kicinski wrote:
> This short set adds a helper to make the implementation of
> two-phase NIC reconfig easier.
> 
> Jakub Kicinski (2):
>   net: add netif_set_real_num_queues() for device reconfig
>   nfp: use netif_set_real_num_queues()

Reviewed-by: Simon Horman <simon.horman@corigine.com>

Re: [PATCH net-next 0/2] net: add netif_set_real_num_queues() for device reconfig

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (refs/heads/master):

On Tue,  3 Aug 2021 06:05:25 -0700 you wrote:
> This short set adds a helper to make the implementation of
> two-phase NIC reconfig easier.
> 
> Jakub Kicinski (2):
>   net: add netif_set_real_num_queues() for device reconfig
>   nfp: use netif_set_real_num_queues()
> 
> [...]

Here is the summary with links:
  - [net-next,1/2] net: add netif_set_real_num_queues() for device reconfig
    https://git.kernel.org/netdev/net-next/c/271e5b7d00ae
  - [net-next,2/2] nfp: use netif_set_real_num_queues()
    https://git.kernel.org/netdev/net-next/c/e874f4557b36

You are awesome, thank you!
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