Subject: Re: [PATCH net 2/2] ixgbe: Allow ixgbe to reset default flow hash

From: Joe Damato <[email-masked]>
Date: Sun, 16 Apr 2023 12:04:18 -0700

On Sun, Apr 16, 2023 at 10:29:36AM -0500, Samudrala, Sridhar wrote:
> 
> 
> On 4/15/2023 12:48 AM, Joe Damato wrote:
> >ethtool uses `ETHTOOL_GRXRINGS` to compute how many queues are supported
> >by RSS. The driver should return the smaller of either:
> >   - The maximum number of RSS queues the device supports, OR
> >   - The number of RX queues configured
> >
> >Prior to this change, running `ethtool -X $iface default` fails if the
> >number of queues configured is larger than the number supported by RSS,
> >even though changing the queue count correctly resets the flowhash to
> >use all supported queues.
> >
> >Other drivers (for example, i40e) will succeed but the flow hash will
> >reset to support the maximum number of queues supported by RSS, even if
> >that amount is smaller than the configured amount.
> >
> >Prior to this change:
> >
> >$ sudo ethtool -L eth1 combined 20
> >$ sudo ethtool -x eth1
> >RX flow hash indirection table for eth1 with 20 RX ring(s):
> >     0:      0     1     2     3     4     5     6     7
> >     8:      8     9    10    11    12    13    14    15
> >    16:      0     1     2     3     4     5     6     7
> >    24:      8     9    10    11    12    13    14    15
> >    32:      0     1     2     3     4     5     6     7
> >...
> >
> >You can see that the flowhash was correctly set to use the maximum
> >number of queues supported by the driver (16).
> >
> >However, asking the NIC to reset to "default" fails:
> >
> >$ sudo ethtool -X eth1 default
> >Cannot set RX flow hash configuration: Invalid argument
> >
> >After this change, the flowhash can be reset to default which will use
> >all of the available RSS queues (16) or the configured queue count,
> >whichever is smaller.
> >
> >Starting with eth1 which has 10 queues and a flowhash distributing to
> >all 10 queues:
> >
> >$ sudo ethtool -x eth1
> >RX flow hash indirection table for eth1 with 10 RX ring(s):
> >     0:      0     1     2     3     4     5     6     7
> >     8:      8     9     0     1     2     3     4     5
> >    16:      6     7     8     9     0     1     2     3
> >...
> >
> >Increasing the queue count to 48 resets the flowhash to distribute to 16
> >queues, as it did before this patch:
> >
> >$ sudo ethtool -L eth1 combined 48
> >$ sudo ethtool -x eth1
> >RX flow hash indirection table for eth1 with 16 RX ring(s):
> >     0:      0     1     2     3     4     5     6     7
> >     8:      8     9    10    11    12    13    14    15
> >    16:      0     1     2     3     4     5     6     7
> >...
> >
> >Due to the other bugfix in this series, the flowhash can be set to use
> >queues 0-5:
> >
> >$ sudo ethtool -X eth1 equal 5
> >$ sudo ethtool -x eth1
> >RX flow hash indirection table for eth1 with 16 RX ring(s):
> >     0:      0     1     2     3     4     0     1     2
> >     8:      3     4     0     1     2     3     4     0
> >    16:      1     2     3     4     0     1     2     3
> >...
> >
> >Due to this bugfix, the flowhash can be reset to default and use 16
> >queues:
> >
> >$ sudo ethtool -X eth1 default
> >$ sudo ethtool -x eth1
> >RX flow hash indirection table for eth1 with 16 RX ring(s):
> >     0:      0     1     2     3     4     5     6     7
> >     8:      8     9    10    11    12    13    14    15
> >    16:      0     1     2     3     4     5     6     7
> >...
> >
> >Signed-off-by: Joe Damato <[email-masked]>
> 
> Thanks for the detailed commit message and steps to reproduce
> and validate the issue.

No worries. Thanks for the review.

> Would suggest changing the title to indicate that this fix is enabling
> setting the RSS indirection table to default value.

OK, sure. I can send a v2 that includes your reviewed tags and changes the
title of this commit (but makes no other changes).

I'll make the new title of this commit ixgbe: Enable setting RSS table to
default values.

Hope that's ok; will send out the v2 shortly.

> Reviewed-by: Sridhar Samudrala <[email-masked]>
> 
> >---
> >  .../net/ethernet/intel/ixgbe/ixgbe_ethtool.c  | 19 ++++++++++---------
> >  1 file changed, 10 insertions(+), 9 deletions(-)
> >
> >diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> >index 821dfd323fa9..0bbad4a5cc2f 100644
> >--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> >+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c
> >@@ -2665,6 +2665,14 @@ static int ixgbe_get_rss_hash_opts(struct ixgbe_adapter *adapter,
> >  	return 0;
> >  }
> >+static int ixgbe_rss_indir_tbl_max(struct ixgbe_adapter *adapter)
> >+{
> >+	if (adapter->hw.mac.type < ixgbe_mac_X550)
> >+		return 16;
> >+	else
> >+		return 64;
> >+}
> >+
> >  static int ixgbe_get_rxnfc(struct net_device *dev, struct ethtool_rxnfc *cmd,
> >  			   u32 *rule_locs)
> >  {
> >@@ -2673,7 +2681,8 @@ static int ixgbe_get_rxnfc(struct net_device *dev, struct ethtool_rxnfc *cmd,
> >  	switch (cmd->cmd) {
> >  	case ETHTOOL_GRXRINGS:
> >-		cmd->data = adapter->num_rx_queues;
> >+		cmd->data = min_t(int, adapter->num_rx_queues,
> >+				  ixgbe_rss_indir_tbl_max(adapter));
> >  		ret = 0;
> >  		break;
> >  	case ETHTOOL_GRXCLSRLCNT:
> >@@ -3075,14 +3084,6 @@ static int ixgbe_set_rxnfc(struct net_device *dev, struct ethtool_rxnfc *cmd)
> >  	return ret;
> >  }
> >-static int ixgbe_rss_indir_tbl_max(struct ixgbe_adapter *adapter)
> >-{
> >-	if (adapter->hw.mac.type < ixgbe_mac_X550)
> >-		return 16;
> >-	else
> >-		return 64;
> >-}
> >-
> >  static u32 ixgbe_get_rxfh_key_size(struct net_device *netdev)
> >  {
> >  	return IXGBE_RSS_KEY_SIZE;