[PATCH net-next 0/2] Count tc-taprio window drops in enetc driver

[PATCH net-next 0/2] Count tc-taprio window drops in enetc driver

[Vladimir Oltean]

This series includes a patch from Po Liu (no longer with NXP) which
counts frames dropped by the tc-taprio offload in ethtool -S and in
ndo_get_stats64. It also contains a preparation patch from myself.

Po Liu (1):
  net: enetc: count the tc-taprio window drops

Vladimir Oltean (1):
  net: enetc: manage ENETC_F_QBV in priv->active_offloads only when
    enabled

 drivers/net/ethernet/freescale/enetc/enetc.c        | 13 +++++++++++--
 drivers/net/ethernet/freescale/enetc/enetc.h        |  2 ++
 .../net/ethernet/freescale/enetc/enetc_ethtool.c    |  2 ++
 drivers/net/ethernet/freescale/enetc/enetc_hw.h     |  1 +
 drivers/net/ethernet/freescale/enetc/enetc_pf.c     |  6 ++----
 drivers/net/ethernet/freescale/enetc/enetc_qos.c    |  6 ++++++
 6 files changed, 24 insertions(+), 6 deletions(-)

-- 
2.25.1

[PATCH net-next 1/2] net: enetc: manage ENETC_F_QBV in priv->active_offloads only when enabled

[Vladimir Oltean]

Future work in this driver would like to look at priv->active_offloads &
ENETC_F_QBV to determine whether a tc-taprio qdisc offload was
installed, but this does not produce the intended effect.

All the other flags in priv->active_offloads are managed dynamically,
except ENETC_F_QBV which is set statically based on the probed SI capability.

This change makes priv->active_offloads & ENETC_F_QBV really track the
presence of a tc-taprio schedule on the port.

Some existing users, like the enetc_sched_speed_set() call from
phylink_mac_link_up(), are best kept using the old logic: the tc-taprio
offload does not re-trigger another link mode resolve, so the scheduler
needs to be functional from the get go, as long as Qbv is supported at
all on the port. So to preserve functionality there, look at the static
station interface capability from pf->si->hw_features instead.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/ethernet/freescale/enetc/enetc_pf.c  | 6 ++----
 drivers/net/ethernet/freescale/enetc/enetc_qos.c | 6 ++++++
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc_pf.c b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
index a0c75c717073..7cccdf54359f 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc_pf.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc_pf.c
@@ -777,9 +777,6 @@ static void enetc_pf_netdev_setup(struct enetc_si *si, struct net_device *ndev,
 
 	ndev->priv_flags |= IFF_UNICAST_FLT;
 
-	if (si->hw_features & ENETC_SI_F_QBV)
-		priv->active_offloads |= ENETC_F_QBV;
-
 	if (si->hw_features & ENETC_SI_F_PSFP && !enetc_psfp_enable(priv)) {
 		priv->active_offloads |= ENETC_F_QCI;
 		ndev->features |= NETIF_F_HW_TC;
@@ -993,7 +990,8 @@ static void enetc_pl_mac_link_up(struct phylink_config *config,
 	int idx;
 
 	priv = netdev_priv(pf->si->ndev);
-	if (priv->active_offloads & ENETC_F_QBV)
+
+	if (pf->si->hw_features & ENETC_SI_F_QBV)
 		enetc_sched_speed_set(priv, speed);
 
 	if (!phylink_autoneg_inband(mode) &&
diff --git a/drivers/net/ethernet/freescale/enetc/enetc_qos.c b/drivers/net/ethernet/freescale/enetc/enetc_qos.c
index 9182631856d5..582a663ed0ba 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc_qos.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc_qos.c
@@ -70,6 +70,9 @@ static int enetc_setup_taprio(struct net_device *ndev,
 		enetc_wr(&priv->si->hw,
 			 ENETC_QBV_PTGCR_OFFSET,
 			 tge & (~ENETC_QBV_TGE));
+
+		priv->active_offloads &= ~ENETC_F_QBV;
+
 		return 0;
 	}
 
@@ -125,6 +128,9 @@ static int enetc_setup_taprio(struct net_device *ndev,
 
 	enetc_cbd_free_data_mem(priv->si, data_size, tmp, &dma);
 
+	if (!err)
+		priv->active_offloads |= ENETC_F_QBV;
+
 	return err;
 }
 
-- 
2.25.1

RE: [PATCH net-next 1/2] net: enetc: manage ENETC_F_QBV in priv->active_offloads only when enabled

[Claudiu Manoil]

> -----Original Message-----
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> Sent: Tuesday, May 10, 2022 7:36 PM
[...]
> Subject: [PATCH net-next 1/2] net: enetc: manage ENETC_F_QBV in priv-
> >active_offloads only when enabled
> 
> Future work in this driver would like to look at priv->active_offloads &
> ENETC_F_QBV to determine whether a tc-taprio qdisc offload was
> installed, but this does not produce the intended effect.
> 
> All the other flags in priv->active_offloads are managed dynamically,
> except ENETC_F_QBV which is set statically based on the probed SI capability.
> 
> This change makes priv->active_offloads & ENETC_F_QBV really track the
> presence of a tc-taprio schedule on the port.
> 
> Some existing users, like the enetc_sched_speed_set() call from
> phylink_mac_link_up(), are best kept using the old logic: the tc-taprio
> offload does not re-trigger another link mode resolve, so the scheduler
> needs to be functional from the get go, as long as Qbv is supported at
> all on the port. So to preserve functionality there, look at the static
> station interface capability from pf->si->hw_features instead.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com>

[PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Vladimir Oltean]

From: Po Liu <Po.Liu@nxp.com>

The enetc scheduler for IEEE 802.1Qbv has 2 options (depending on
PTGCR[TG_DROP_DISABLE]) when we attempt to send an oversized packet
which will never fit in its allotted time slot for its traffic class:
either block the entire port due to head-of-line blocking, or drop the
packet and set a bit in the writeback format of the transmit buffer
descriptor, allowing other packets to be sent.

We obviously choose the second option in the driver, but we do not
detect the drop condition, so from the perspective of the network stack,
the packet is sent and no error counter is incremented.

This change checks the writeback of the TX BD when tc-taprio is enabled,
and increments a specific ethtool statistics counter and a generic
"tx_dropped" counter in ndo_get_stats64.

Signed-off-by: Po Liu <Po.Liu@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/ethernet/freescale/enetc/enetc.c        | 13 +++++++++++--
 drivers/net/ethernet/freescale/enetc/enetc.h        |  2 ++
 .../net/ethernet/freescale/enetc/enetc_ethtool.c    |  2 ++
 drivers/net/ethernet/freescale/enetc/enetc_hw.h     |  1 +
 4 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index d6930a797c6c..4470a4a3e4c3 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -172,7 +172,8 @@ static int enetc_map_tx_buffs(struct enetc_bdr *tx_ring, struct sk_buff *skb)
 	}
 
 	tx_swbd->do_twostep_tstamp = do_twostep_tstamp;
-	tx_swbd->check_wb = tx_swbd->do_twostep_tstamp;
+	tx_swbd->qbv_en = !!(priv->active_offloads & ENETC_F_QBV);
+	tx_swbd->check_wb = tx_swbd->do_twostep_tstamp || tx_swbd->qbv_en;
 
 	if (do_vlan || do_onestep_tstamp || do_twostep_tstamp)
 		flags |= ENETC_TXBD_FLAGS_EX;
@@ -792,9 +793,9 @@ static void enetc_recycle_xdp_tx_buff(struct enetc_bdr *tx_ring,
 
 static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
 {
+	int tx_frm_cnt = 0, tx_byte_cnt = 0, tx_win_drop = 0;
 	struct net_device *ndev = tx_ring->ndev;
 	struct enetc_ndev_priv *priv = netdev_priv(ndev);
-	int tx_frm_cnt = 0, tx_byte_cnt = 0;
 	struct enetc_tx_swbd *tx_swbd;
 	int i, bds_to_clean;
 	bool do_twostep_tstamp;
@@ -821,6 +822,10 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
 						    &tstamp);
 				do_twostep_tstamp = true;
 			}
+
+			if (tx_swbd->qbv_en &&
+			    txbd->wb.status & ENETC_TXBD_STATS_WIN)
+				tx_win_drop++;
 		}
 
 		if (tx_swbd->is_xdp_tx)
@@ -873,6 +878,7 @@ static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int napi_budget)
 	tx_ring->next_to_clean = i;
 	tx_ring->stats.packets += tx_frm_cnt;
 	tx_ring->stats.bytes += tx_byte_cnt;
+	tx_ring->stats.win_drop += tx_win_drop;
 
 	if (unlikely(tx_frm_cnt && netif_carrier_ok(ndev) &&
 		     __netif_subqueue_stopped(ndev, tx_ring->index) &&
@@ -2552,6 +2558,7 @@ struct net_device_stats *enetc_get_stats(struct net_device *ndev)
 	struct enetc_ndev_priv *priv = netdev_priv(ndev);
 	struct net_device_stats *stats = &ndev->stats;
 	unsigned long packets = 0, bytes = 0;
+	unsigned long tx_dropped = 0;
 	int i;
 
 	for (i = 0; i < priv->num_rx_rings; i++) {
@@ -2567,10 +2574,12 @@ struct net_device_stats *enetc_get_stats(struct net_device *ndev)
 	for (i = 0; i < priv->num_tx_rings; i++) {
 		packets += priv->tx_ring[i]->stats.packets;
 		bytes	+= priv->tx_ring[i]->stats.bytes;
+		tx_dropped += priv->tx_ring[i]->stats.win_drop;
 	}
 
 	stats->tx_packets = packets;
 	stats->tx_bytes = bytes;
+	stats->tx_dropped = tx_dropped;
 
 	return stats;
 }
diff --git a/drivers/net/ethernet/freescale/enetc/enetc.h b/drivers/net/ethernet/freescale/enetc/enetc.h
index 68d806dc3701..29922c20531f 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.h
+++ b/drivers/net/ethernet/freescale/enetc/enetc.h
@@ -36,6 +36,7 @@ struct enetc_tx_swbd {
 	u8 is_eof:1;
 	u8 is_xdp_tx:1;
 	u8 is_xdp_redirect:1;
+	u8 qbv_en:1;
 };
 
 #define ENETC_RX_MAXFRM_SIZE	ENETC_MAC_MAXFRM_SIZE
@@ -72,6 +73,7 @@ struct enetc_ring_stats {
 	unsigned int xdp_redirect_sg;
 	unsigned int recycles;
 	unsigned int recycle_failures;
+	unsigned int win_drop;
 };
 
 struct enetc_xdp_data {
diff --git a/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c b/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c
index 60ec64bfb3f0..ff872e40ce85 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc_ethtool.c
@@ -204,6 +204,7 @@ static const char tx_ring_stats[][ETH_GSTRING_LEN] = {
 	"Tx ring %2d frames",
 	"Tx ring %2d XDP frames",
 	"Tx ring %2d XDP drops",
+	"Tx window drop %2d frames",
 };
 
 static int enetc_get_sset_count(struct net_device *ndev, int sset)
@@ -279,6 +280,7 @@ static void enetc_get_ethtool_stats(struct net_device *ndev,
 		data[o++] = priv->tx_ring[i]->stats.packets;
 		data[o++] = priv->tx_ring[i]->stats.xdp_tx;
 		data[o++] = priv->tx_ring[i]->stats.xdp_tx_drops;
+		data[o++] = priv->tx_ring[i]->stats.win_drop;
 	}
 
 	for (i = 0; i < priv->num_rx_rings; i++) {
diff --git a/drivers/net/ethernet/freescale/enetc/enetc_hw.h b/drivers/net/ethernet/freescale/enetc/enetc_hw.h
index ce5b677e8c2f..647c87f73bf7 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc_hw.h
+++ b/drivers/net/ethernet/freescale/enetc/enetc_hw.h
@@ -543,6 +543,7 @@ enum enetc_txbd_flags {
 	ENETC_TXBD_FLAGS_EX = BIT(6),
 	ENETC_TXBD_FLAGS_F = BIT(7)
 };
+#define ENETC_TXBD_STATS_WIN	BIT(7)
 #define ENETC_TXBD_TXSTART_MASK GENMASK(24, 0)
 #define ENETC_TXBD_FLAGS_OFFSET 24
 
-- 
2.25.1

RE: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Claudiu Manoil]

> -----Original Message-----
> From: Vladimir Oltean <vladimir.oltean@nxp.com>
> Sent: Tuesday, May 10, 2022 7:36 PM
[...]
> Subject: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops
> 
> From: Po Liu <Po.Liu@nxp.com>
> 
> The enetc scheduler for IEEE 802.1Qbv has 2 options (depending on
> PTGCR[TG_DROP_DISABLE]) when we attempt to send an oversized packet
> which will never fit in its allotted time slot for its traffic class:
> either block the entire port due to head-of-line blocking, or drop the
> packet and set a bit in the writeback format of the transmit buffer
> descriptor, allowing other packets to be sent.
> 
> We obviously choose the second option in the driver, but we do not
> detect the drop condition, so from the perspective of the network stack,
> the packet is sent and no error counter is incremented.
> 
> This change checks the writeback of the TX BD when tc-taprio is enabled,
> and increments a specific ethtool statistics counter and a generic
> "tx_dropped" counter in ndo_get_stats64.
> 
> Signed-off-by: Po Liu <Po.Liu@nxp.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>

Reviewed-by: Claudiu Manoil <claudiu.manoil@nxp.com>

Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Jakub Kicinski]

On Tue, 10 May 2022 19:36:15 +0300 Vladimir Oltean wrote:
> From: Po Liu <Po.Liu@nxp.com>
> 
> The enetc scheduler for IEEE 802.1Qbv has 2 options (depending on
> PTGCR[TG_DROP_DISABLE]) when we attempt to send an oversized packet
> which will never fit in its allotted time slot for its traffic class:
> either block the entire port due to head-of-line blocking, or drop the
> packet and set a bit in the writeback format of the transmit buffer
> descriptor, allowing other packets to be sent.
> 
> We obviously choose the second option in the driver, but we do not
> detect the drop condition, so from the perspective of the network stack,
> the packet is sent and no error counter is incremented.
> 
> This change checks the writeback of the TX BD when tc-taprio is enabled,
> and increments a specific ethtool statistics counter and a generic
> "tx_dropped" counter in ndo_get_stats64.

Is there no MIB attribute in the standard for such drops?

The semantics seem petty implementation-independent can we put it into
some structured ethtool stats instead?

Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Vladimir Oltean]

On Wed, May 11, 2022 at 03:27:40PM -0700, Jakub Kicinski wrote:
> On Tue, 10 May 2022 19:36:15 +0300 Vladimir Oltean wrote:
> > From: Po Liu <Po.Liu@nxp.com>
> > 
> > The enetc scheduler for IEEE 802.1Qbv has 2 options (depending on
> > PTGCR[TG_DROP_DISABLE]) when we attempt to send an oversized packet
> > which will never fit in its allotted time slot for its traffic class:
> > either block the entire port due to head-of-line blocking, or drop the
> > packet and set a bit in the writeback format of the transmit buffer
> > descriptor, allowing other packets to be sent.
> > 
> > We obviously choose the second option in the driver, but we do not
> > detect the drop condition, so from the perspective of the network stack,
> > the packet is sent and no error counter is incremented.
> > 
> > This change checks the writeback of the TX BD when tc-taprio is enabled,
> > and increments a specific ethtool statistics counter and a generic
> > "tx_dropped" counter in ndo_get_stats64.
> 
> Is there no MIB attribute in the standard for such drops?
> 
> The semantics seem petty implementation-independent can we put it into
> some structured ethtool stats instead?

My copy of IEEE 802.1Q-2018 talks about the following MIB table entries
in clause 17.2.22 Structure of the IEEE8021-ST-MIB:

ieee8021STMaxSDU subtree
  ieee8021STMaxSDUTable
  ieee8021STTrafficClass
  ieee8021STMaxSDU
  ieee8021TransmissionOverrun

ieee8021STParameters
  ieee8021STParametersTable
  ieee8021STGateEnabled
  ieee8021STAdminGateStates
  ieee8021STOperGateStates
  ieee8021STAdminControlListLength
  ieee8021STOperControlListLength
  ieee8021STAdminControlList
  ieee8021STOperControlList
  ieee8021STAdminCycleTimeNumerator
  ieee8021STAdminCycleTimeDenominator
  ieee8021STOperCycleTimeNumerator
  ieee8021STOperCycleTimeDenominator
  ieee8021STAdminCycleTimeExtension
  ieee8021STOperCycleTimeExtension
  ieee8021STAdminBaseTime
  ieee8021STOperBaseTime
  ieee8021STConfigChange
  ieee8021STConfigChangeTime
  ieee8021STTickGranularity
  ieee8021STCurrentTime
  ieee802STConfigPending
  ieee8021STSupportedListMax

The only entry that is a counter in the Scheduled Traffic MIB is TransmissionOverrun,
but that isn't what this is. Instead, this would be a TransmissionOverrunAvoidedByDropping,
for which there appears to be no standardization.

Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Jakub Kicinski]

On Wed, 11 May 2022 22:57:46 +0000 Vladimir Oltean wrote:
> The only entry that is a counter in the Scheduled Traffic MIB is TransmissionOverrun,
> but that isn't what this is. Instead, this would be a TransmissionOverrunAvoidedByDropping,
> for which there appears to be no standardization.

TransmissionOversized? There's no standardization in terms of IEEE but
the semantics seem pretty clear right? The packet is longer than the
entire window so it can never go out?

Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Vladimir Oltean]

On Wed, May 11, 2022 at 04:13:46PM -0700, Jakub Kicinski wrote:
> On Wed, 11 May 2022 22:57:46 +0000 Vladimir Oltean wrote:
> > The only entry that is a counter in the Scheduled Traffic MIB is TransmissionOverrun,
> > but that isn't what this is. Instead, this would be a TransmissionOverrunAvoidedByDropping,
> > for which there appears to be no standardization.
> 
> TransmissionOversized? There's no standardization in terms of IEEE but
> the semantics seem pretty clear right? The packet is longer than the
> entire window so it can never go out?

Yes, so what are you saying? Become the ad-hoc standards body for
scheduled traffic?

Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Jakub Kicinski]

On Wed, 11 May 2022 23:17:46 +0000 Vladimir Oltean wrote:
> On Wed, May 11, 2022 at 04:13:46PM -0700, Jakub Kicinski wrote:
> > On Wed, 11 May 2022 22:57:46 +0000 Vladimir Oltean wrote:  
> > > The only entry that is a counter in the Scheduled Traffic MIB is TransmissionOverrun,
> > > but that isn't what this is. Instead, this would be a TransmissionOverrunAvoidedByDropping,
> > > for which there appears to be no standardization.  
> > 
> > TransmissionOversized? There's no standardization in terms of IEEE but
> > the semantics seem pretty clear right? The packet is longer than the
> > entire window so it can never go out?  
> 
> Yes, so what are you saying? Become the ad-hoc standards body for
> scheduled traffic?

We can argue semantics but there doesn't need to be a "standards body"
to add a structured stat in ethtool [1]. When next gen of enetc comes
out you'll likely try to use the same stat name or reuse the entire
driver. So you are already defining uAPI for your users, it's only 
a question of scope at which the uAPI is defined.

What I'm not sure of is what to attach that statistic to. You have it
per ring and we famously don't have per ring APIs, so whatever, let 
me apply as is and move on :)

[1] Coincidentally I plan to add a "real link loss" statistic there
because AFAICR IEEE doesn't have a stat for it, and carrier_changes
count software events so it's meaningless to teams trying to track
cable issues.

Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Vladimir Oltean]

On Wed, May 11, 2022 at 04:36:55PM -0700, Jakub Kicinski wrote:
> On Wed, 11 May 2022 23:17:46 +0000 Vladimir Oltean wrote:
> > On Wed, May 11, 2022 at 04:13:46PM -0700, Jakub Kicinski wrote:
> > > On Wed, 11 May 2022 22:57:46 +0000 Vladimir Oltean wrote:
> > > > The only entry that is a counter in the Scheduled Traffic MIB is TransmissionOverrun,
> > > > but that isn't what this is. Instead, this would be a TransmissionOverrunAvoidedByDropping,
> > > > for which there appears to be no standardization.
> > >
> > > TransmissionOversized? There's no standardization in terms of IEEE but
> > > the semantics seem pretty clear right? The packet is longer than the
> > > entire window so it can never go out?
> >
> > Yes, so what are you saying? Become the ad-hoc standards body for
> > scheduled traffic?
>
> We can argue semantics but there doesn't need to be a "standards body"
> to add a structured stat in ethtool [1]. When next gen of enetc comes
> out you'll likely try to use the same stat name or reuse the entire
> driver. So you are already defining uAPI for your users, it's only
> a question of scope at which the uAPI is defined.

The trouble with over-standardization is that with a different driver
that would use this ad-hoc structure for parts of it, you never know if
a counter is 0 because it's 0 or because it's not implemented.
As unstructured as the plain ethtool -S might be, at least if you see a
counter there, you can expect that it actually counts something.

> What I'm not sure of is what to attach that statistic to. You have it
> per ring and we famously don't have per ring APIs, so whatever, let
> me apply as is and move on :)

It would probably have to be per traffic class, since the media
reservation gates are per traffic class (TX rings have a configurable
mapping with traffic classes). Although an aggregate counter would also
be plausible. Who knows? I haven't seen this specific counter being
reported by the LS1028A switch, for example (I'll have to check what
increments on blocked transmission overruns).

> [1] Coincidentally I plan to add a "real link loss" statistic there
> because AFAICR IEEE doesn't have a stat for it, and carrier_changes
> count software events so it's meaningless to teams trying to track
> cable issues.

I didn't quite get what's wrong with the carrier_changes sysfs counter,
and how "real link loss" would be implemented differently/more usefully?
At least with phylib/phylink users, netif_carrier_on() + netif_carrier_off()
are called exactly on phydev->phy_link_change() events.
Are there other callers of netif_carrier_*() that pollute this counter
and make it useless for reliable debugging?

Re: [PATCH net-next 2/2] net: enetc: count the tc-taprio window drops

[Jakub Kicinski]

On Thu, 12 May 2022 00:20:18 +0000 Vladimir Oltean wrote:
> > We can argue semantics but there doesn't need to be a "standards body"
> > to add a structured stat in ethtool [1]. When next gen of enetc comes
> > out you'll likely try to use the same stat name or reuse the entire
> > driver. So you are already defining uAPI for your users, it's only
> > a question of scope at which the uAPI is defined.  
> 
> The trouble with over-standardization is that with a different driver
> that would use this ad-hoc structure for parts of it, you never know if
> a counter is 0 because it's 0 or because it's not implemented.
> As unstructured as the plain ethtool -S might be, at least if you see a
> counter there, you can expect that it actually counts something.

That's solved with the netlink ethtool stats. What's not repored by the
driver is not reported to user space. Grep for ETHTOOL_STAT_NOT_SET.
Maybe not beautiful but works.

> > What I'm not sure of is what to attach that statistic to. You have it
> > per ring and we famously don't have per ring APIs, so whatever, let
> > me apply as is and move on :)  
> 
> It would probably have to be per traffic class, since the media
> reservation gates are per traffic class (TX rings have a configurable
> mapping with traffic classes). Although an aggregate counter would also
> be plausible. Who knows?

Well, users sometimes know what they want but the days when the kernel
was written by its users are long gone. Or maybe that's just a perfect
example of the "good old days" fallacy :)

> I haven't seen this specific counter being reported by the LS1028A
> switch, for example (I'll have to check what increments on blocked
> transmission overruns).
> 
> > [1] Coincidentally I plan to add a "real link loss" statistic there
> > because AFAICR IEEE doesn't have a stat for it, and carrier_changes
> > count software events so it's meaningless to teams trying to track
> > cable issues.  
> 
> I didn't quite get what's wrong with the carrier_changes sysfs
> counter, and how "real link loss" would be implemented
> differently/more usefully? At least with phylib/phylink users,
> netif_carrier_on() + netif_carrier_off() are called exactly on
> phydev->phy_link_change() events. Are there other callers of
> netif_carrier_*() that pollute this counter and make it useless for
> reliable debugging?

Yup, drivers will do a netif_carrier_off() to stop Tx and prevent
the timeout watchdog from kicking in while they are doing some form 
of reconfig (ethtool -L / -G etc.).

I guess we can add a special API for taking things down without
bumping the counter. Since drivers I work with already report an
ethtool -S stat from the device for "PHY really went down" my first
instinct was a better ethtool stat...

Re: [PATCH net-next 0/2] Count tc-taprio window drops in enetc driver

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Tue, 10 May 2022 19:36:13 +0300 you wrote:
> This series includes a patch from Po Liu (no longer with NXP) which
> counts frames dropped by the tc-taprio offload in ethtool -S and in
> ndo_get_stats64. It also contains a preparation patch from myself.
> 
> Po Liu (1):
>   net: enetc: count the tc-taprio window drops
> 
> [...]

Here is the summary with links:
  - [net-next,1/2] net: enetc: manage ENETC_F_QBV in priv->active_offloads only when enabled
    https://git.kernel.org/netdev/net-next/c/32bf8e1f6fb9
  - [net-next,2/2] net: enetc: count the tc-taprio window drops
    https://git.kernel.org/netdev/net-next/c/285e8dedb4bd

You are awesome, thank you!
-- 
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