iavf: kill "legacy-rx" for good

Ever since build_skb() became stable, the old way with allocating an skb
for storing the headers separately, which will be then copied manually,
was slower, less flexible, and thus obsolete.

* It had higher pressure on MM since it actually allocates new pages,
  which then get split and refcount-biased (NAPI page cache);
* It implies memcpy() of packet headers (40+ bytes per each frame);
* the actual header length was calculated via eth_get_headlen(), which
  invokes Flow Dissector and thus wastes a bunch of CPU cycles;
* XDP makes it even more weird since it requires headroom for long and
  also tailroom for some time (since mbuf landed). Take a look at the
  ice driver, which is built around work-arounds to make XDP work with
  it.

Even on some quite low-end hardware (not a common case for 100G NICs) it
was performing worse.
The only advantage "legacy-rx" had is that it didn't require any
reserved headroom and tailroom. But iavf didn't use this, as it always
splits pages into two halves of 2k, while that save would only be useful
when striding. And again, XDP effectively removes that sole pro.

There's a train of features to land in IAVF soon: Page Pool, XDP, XSk,
multi-buffer etc. Each new would require adding more and more Danse
Macabre for absolutely no reason, besides making hotpath less and less
effective.
Remove the "feature" with all the related code. This includes at least
one very hot branch (typically hit on each new frame), which was either
always-true or always-false at least for a complete NAPI bulk of 64
frames, the whole private flags cruft, and so on. Some stats:

Function: add/remove: 0/4 grow/shrink: 0/7 up/down: 0/-721 (-721)
RO Data: add/remove: 0/1 grow/shrink: 0/0 up/down: 0/-40 (-40)

Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

1 files changed, 0 insertions, 140 deletions

diff --git a/drivers/net/ethernet/intel/iavf/iavf_ethtool.c b/drivers/net/ethernet/intel/iavf/iavf_ethtool.c
index 378c3e9ddf9d..52273f7eab2c 100644
--- a/drivers/net/ethernet/intel/iavf/iavf_ethtool.c
+++ b/drivers/net/ethernet/intel/iavf/iavf_ethtool.c
@@ -240,29 +240,6 @@ static const struct iavf_stats iavf_gstrings_stats[] = {
 
 #define IAVF_QUEUE_STATS_LEN	ARRAY_SIZE(iavf_gstrings_queue_stats)
 
-/* For now we have one and only one private flag and it is only defined
- * when we have support for the SKIP_CPU_SYNC DMA attribute.  Instead
- * of leaving all this code sitting around empty we will strip it unless
- * our one private flag is actually available.
- */
-struct iavf_priv_flags {
-	char flag_string[ETH_GSTRING_LEN];
-	u32 flag;
-	bool read_only;
-};
-
-#define IAVF_PRIV_FLAG(_name, _flag, _read_only) { \
-	.flag_string = _name, \
-	.flag = _flag, \
-	.read_only = _read_only, \
-}
-
-static const struct iavf_priv_flags iavf_gstrings_priv_flags[] = {
-	IAVF_PRIV_FLAG("legacy-rx", IAVF_FLAG_LEGACY_RX, 0),
-};
-
-#define IAVF_PRIV_FLAGS_STR_LEN ARRAY_SIZE(iavf_gstrings_priv_flags)
-
 /**
  * iavf_get_link_ksettings - Get Link Speed and Duplex settings
  * @netdev: network interface device structure
@@ -342,8 +319,6 @@ static int iavf_get_sset_count(struct net_device *netdev, int sset)
 		return IAVF_STATS_LEN +
 			(IAVF_QUEUE_STATS_LEN * 2 *
 			 netdev->real_num_tx_queues);
-	else if (sset == ETH_SS_PRIV_FLAGS)
-		return IAVF_PRIV_FLAGS_STR_LEN;
 	else
 		return -EINVAL;
 }
@@ -386,21 +361,6 @@ static void iavf_get_ethtool_stats(struct net_device *netdev,
 }
 
 /**
- * iavf_get_priv_flag_strings - Get private flag strings
- * @netdev: network interface device structure
- * @data: buffer for string data
- *
- * Builds the private flags string table
- **/
-static void iavf_get_priv_flag_strings(struct net_device *netdev, u8 *data)
-{
-	unsigned int i;
-
-	for (i = 0; i < IAVF_PRIV_FLAGS_STR_LEN; i++)
-		ethtool_puts(&data, iavf_gstrings_priv_flags[i].flag_string);
-}
-
-/**
  * iavf_get_stat_strings - Get stat strings
  * @netdev: network interface device structure
  * @data: buffer for string data
@@ -438,109 +398,12 @@ static void iavf_get_strings(struct net_device *netdev, u32 sset, u8 *data)
 	case ETH_SS_STATS:
 		iavf_get_stat_strings(netdev, data);
 		break;
-	case ETH_SS_PRIV_FLAGS:
-		iavf_get_priv_flag_strings(netdev, data);
-		break;
 	default:
 		break;
 	}
 }
 
 /**
- * iavf_get_priv_flags - report device private flags
- * @netdev: network interface device structure
- *
- * The get string set count and the string set should be matched for each
- * flag returned.  Add new strings for each flag to the iavf_gstrings_priv_flags
- * array.
- *
- * Returns a u32 bitmap of flags.
- **/
-static u32 iavf_get_priv_flags(struct net_device *netdev)
-{
-	struct iavf_adapter *adapter = netdev_priv(netdev);
-	u32 i, ret_flags = 0;
-
-	for (i = 0; i < IAVF_PRIV_FLAGS_STR_LEN; i++) {
-		const struct iavf_priv_flags *priv_flags;
-
-		priv_flags = &iavf_gstrings_priv_flags[i];
-
-		if (priv_flags->flag & adapter->flags)
-			ret_flags |= BIT(i);
-	}
-
-	return ret_flags;
-}
-
-/**
- * iavf_set_priv_flags - set private flags
- * @netdev: network interface device structure
- * @flags: bit flags to be set
- **/
-static int iavf_set_priv_flags(struct net_device *netdev, u32 flags)
-{
-	struct iavf_adapter *adapter = netdev_priv(netdev);
-	u32 orig_flags, new_flags, changed_flags;
-	int ret = 0;
-	u32 i;
-
-	orig_flags = READ_ONCE(adapter->flags);
-	new_flags = orig_flags;
-
-	for (i = 0; i < IAVF_PRIV_FLAGS_STR_LEN; i++) {
-		const struct iavf_priv_flags *priv_flags;
-
-		priv_flags = &iavf_gstrings_priv_flags[i];
-
-		if (flags & BIT(i))
-			new_flags |= priv_flags->flag;
-		else
-			new_flags &= ~(priv_flags->flag);
-
-		if (priv_flags->read_only &&
-		    ((orig_flags ^ new_flags) & ~BIT(i)))
-			return -EOPNOTSUPP;
-	}
-
-	/* Before we finalize any flag changes, any checks which we need to
-	 * perform to determine if the new flags will be supported should go
-	 * here...
-	 */
-
-	/* Compare and exchange the new flags into place. If we failed, that
-	 * is if cmpxchg returns anything but the old value, this means
-	 * something else must have modified the flags variable since we
-	 * copied it. We'll just punt with an error and log something in the
-	 * message buffer.
-	 */
-	if (cmpxchg(&adapter->flags, orig_flags, new_flags) != orig_flags) {
-		dev_warn(&adapter->pdev->dev,
-			 "Unable to update adapter->flags as it was modified by another thread...\n");
-		return -EAGAIN;
-	}
-
-	changed_flags = orig_flags ^ new_flags;
-
-	/* Process any additional changes needed as a result of flag changes.
-	 * The changed_flags value reflects the list of bits that were changed
-	 * in the code above.
-	 */
-
-	/* issue a reset to force legacy-rx change to take effect */
-	if (changed_flags & IAVF_FLAG_LEGACY_RX) {
-		if (netif_running(netdev)) {
-			iavf_schedule_reset(adapter, IAVF_FLAG_RESET_NEEDED);
-			ret = iavf_wait_for_reset(adapter);
-			if (ret)
-				netdev_warn(netdev, "Changing private flags timeout or interrupted waiting for reset");
-		}
-	}
-
-	return ret;
-}
-
-/**
  * iavf_get_msglevel - Get debug message level
  * @netdev: network interface device structure
  *
@@ -585,7 +448,6 @@ static void iavf_get_drvinfo(struct net_device *netdev,
 	strscpy(drvinfo->driver, iavf_driver_name, 32);
 	strscpy(drvinfo->fw_version, "N/A", 4);
 	strscpy(drvinfo->bus_info, pci_name(adapter->pdev), 32);
-	drvinfo->n_priv_flags = IAVF_PRIV_FLAGS_STR_LEN;
 }
 
 /**
@@ -1995,8 +1857,6 @@ static const struct ethtool_ops iavf_ethtool_ops = {
 	.get_strings		= iavf_get_strings,
 	.get_ethtool_stats	= iavf_get_ethtool_stats,
 	.get_sset_count		= iavf_get_sset_count,
-	.get_priv_flags		= iavf_get_priv_flags,
-	.set_priv_flags		= iavf_set_priv_flags,
 	.get_msglevel		= iavf_get_msglevel,
 	.set_msglevel		= iavf_set_msglevel,
 	.get_coalesce		= iavf_get_coalesce,