When running "xdp-bench tx eno0" to test the XDP_TX feature of ENETC
on LS1028A, it was found that if the command was re-run multiple times,
Rx could not receive the frames, and the result of xdo-bench showed
that the rx rate was 0.

root@ls1028ardb:~# ./xdp-bench tx eno0
Hairpinning (XDP_TX) packets on eno0 (ifindex 3; driver fsl_enetc)
Summary                      2046 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s

By observing the Rx PIR and CIR registers, we found that CIR is always
equal to 0x7FF and PIR is always 0x7FE, which means that the Rx ring
is full and can no longer accommodate other Rx frames. Therefore, we
can conclude that the problem is caused by the Rx BD ring not being
cleaned up.

Further analysis of the code revealed that the Rx BD ring will only
be cleaned if the "cleaned_cnt > xdp_tx_in_flight" condition is met.
Therefore, some debug logs were added to the driver and the current
values of cleaned_cnt and xdp_tx_in_flight were printed when the Rx
BD ring was full. The logs are as follows.

[  178.762419] [XDP TX] >> cleaned_cnt:1728, xdp_tx_in_flight:2140
[  178.771387] [XDP TX] >> cleaned_cnt:1941, xdp_tx_in_flight:2110
[  178.776058] [XDP TX] >> cleaned_cnt:1792, xdp_tx_in_flight:2110

From the results, we can see that the max value of xdp_tx_in_flight
has reached 2140. However, the size of the Rx BD ring is only 2048.
This is incredible, so we checked the code again and found that
xdp_tx_in_flight did not drop to 0 when the bpf program was uninstalled
and it was not reset when the bfp program was installed again. The
root cause is that the IRQ is disabled too early in enetc_stop(),
resulting in enetc_recycle_xdp_tx_buff() not being called, therefore,
xdp_tx_in_flight is not cleared.

Fixes: ff58fda09096 ("net: enetc: prioritize ability to go down over packet processing")
Cc: stable@vger.kernel.org
Signed-off-by: Wei Fang <wei.fang@nxp.com>
---
v2 changes:
1. Modify the titile and rephrase the commit meesage.
2. Use the new solution as described in the title
---
 drivers/net/ethernet/freescale/enetc/enetc.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/freescale/enetc/enetc.c b/drivers/net/ethernet/freescale/enetc/enetc.c
index 138c0a36f033..906f0edbfef8 100644
--- a/drivers/net/ethernet/freescale/enetc/enetc.c
+++ b/drivers/net/ethernet/freescale/enetc/enetc.c
@@ -2468,8 +2468,6 @@ void enetc_start(struct net_device *ndev)
 
 	enetc_setup_interrupts(priv);
 
-	enetc_enable_tx_bdrs(priv);
-
 	for (i = 0; i < priv->bdr_int_num; i++) {
 		int irq = pci_irq_vector(priv->si->pdev,
 					 ENETC_BDR_INT_BASE_IDX + i);
@@ -2478,6 +2476,8 @@ void enetc_start(struct net_device *ndev)
 		enable_irq(irq);
 	}
 
+	enetc_enable_tx_bdrs(priv);
+
 	enetc_enable_rx_bdrs(priv);
 
 	netif_tx_start_all_queues(ndev);
@@ -2546,6 +2546,10 @@ void enetc_stop(struct net_device *ndev)
 
 	enetc_disable_rx_bdrs(priv);
 
+	enetc_wait_bdrs(priv);
+
+	enetc_disable_tx_bdrs(priv);
+
 	for (i = 0; i < priv->bdr_int_num; i++) {
 		int irq = pci_irq_vector(priv->si->pdev,
 					 ENETC_BDR_INT_BASE_IDX + i);
@@ -2555,10 +2559,6 @@ void enetc_stop(struct net_device *ndev)
 		napi_disable(&priv->int_vector[i]->napi);
 	}
 
-	enetc_wait_bdrs(priv);
-
-	enetc_disable_tx_bdrs(priv);
-
 	enetc_clear_interrupts(priv);
 }
 EXPORT_SYMBOL_GPL(enetc_stop);
-- 
2.34.1

On Sun, Sep 29, 2024 at 10:45:06AM +0800, Wei Fang wrote:
> When running "xdp-bench tx eno0" to test the XDP_TX feature of ENETC
> on LS1028A, it was found that if the command was re-run multiple times,
> Rx could not receive the frames, and the result of xdo-bench showed
> that the rx rate was 0.
> 
> root@ls1028ardb:~# ./xdp-bench tx eno0
> Hairpinning (XDP_TX) packets on eno0 (ifindex 3; driver fsl_enetc)
> Summary                      2046 rx/s                  0 err,drop/s
> Summary                         0 rx/s                  0 err,drop/s
> Summary                         0 rx/s                  0 err,drop/s
> Summary                         0 rx/s                  0 err,drop/s
> 
> By observing the Rx PIR and CIR registers, we found that CIR is always
> equal to 0x7FF and PIR is always 0x7FE, which means that the Rx ring
> is full and can no longer accommodate other Rx frames. Therefore, we
> can conclude that the problem is caused by the Rx BD ring not being
> cleaned up.
> 
> Further analysis of the code revealed that the Rx BD ring will only
> be cleaned if the "cleaned_cnt > xdp_tx_in_flight" condition is met.
> Therefore, some debug logs were added to the driver and the current
> values of cleaned_cnt and xdp_tx_in_flight were printed when the Rx
> BD ring was full. The logs are as follows.
> 
> [  178.762419] [XDP TX] >> cleaned_cnt:1728, xdp_tx_in_flight:2140
> [  178.771387] [XDP TX] >> cleaned_cnt:1941, xdp_tx_in_flight:2110
> [  178.776058] [XDP TX] >> cleaned_cnt:1792, xdp_tx_in_flight:2110
> 
> From the results, we can see that the max value of xdp_tx_in_flight
> has reached 2140. However, the size of the Rx BD ring is only 2048.
> This is incredible, so we checked the code again and found that
> xdp_tx_in_flight did not drop to 0 when the bpf program was uninstalled
> and it was not reset when the bfp program was installed again. The
> root cause is that the IRQ is disabled too early in enetc_stop(),
> resulting in enetc_recycle_xdp_tx_buff() not being called, therefore,
> xdp_tx_in_flight is not cleared.
> 
> Fixes: ff58fda09096 ("net: enetc: prioritize ability to go down over packet processing")
> Cc: stable@vger.kernel.org
> Signed-off-by: Wei Fang <wei.fang@nxp.com>
> ---
> v2 changes:
> 1. Modify the titile and rephrase the commit meesage.
> 2. Use the new solution as described in the title
> ---

I gave this another test under a bit different set of circumstances this time,
and I'm confident that there are still problems, which I haven't identified
though (yet).

With 64 byte frames at 2.5 Gbps, I see this going on:

$ xdp-bench tx eno0 &
$ while :; do taskset $((1 << 0)) hwstamp_ctl -i eno0 -r 1 && sleep 1 && taskset $((1 << 0)) hwstamp_ctl -i eno0 -r 0 && sleep 1; done
current settings:
tx_type 0
rx_filter 0
new settings:
tx_type 0
rx_filter 1
Summary                 1,556,952 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s
Summary                         0 rx/s                  0 err,drop/s
current settings:
tx_type 0
rx_filter 1
Summary                         0 rx/s                  0 err,drop/s
[  883.780346] fsl_enetc 0000:00:00.0 eno0: timeout for tx ring #6 clear (its RX ring has 2072 XDP_TX frames in flight)
new settings:
tx_type 0
rx_filter 0
Summary                     1,027 rx/s                  0 err,drop/s
current settings:
tx_type 0
rx_filter 0
Summary                         0 rx/s                  0 err,drop/s

which looks like the symptoms that the patch tries to solve.

My previous testing was with 390 byte frames, and this did not happen.

Please do not merge this.