netdev - Re: [PATCH net 3/3] net: enetc: reset xdp_tx_in

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Message-ID: <ZuwHHx2HiRlRipkw@test-OptiPlex-Tower-Plus-7010>
Date: Thu, 19 Sep 2024 16:42:31 +0530
From: Subbaraya Sundeep <sbhatta@...vell.com>
To: Wei Fang <wei.fang@....com>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <claudiu.manoil@....com>,
        <vladimir.oltean@....com>, <ast@...nel.org>, <daniel@...earbox.net>,
        <hawk@...nel.org>, <john.fastabend@...il.com>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>, <stable@...r.kernel.org>, <imx@...ts.linux.dev>
Subject: Re: [PATCH net 3/3] net: enetc: reset xdp_tx_in_flight when updating
 bpf program

On 2024-09-19 at 14:11:04, Wei Fang (wei.fang@....com) 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@...028ardb:~# ./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, it
> is obvious that the RX BD ring has not been 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 maximum value of xdp_tx_in_flight
> has reached 2140. However, the size of the Rx BD ring is only 2048. This
> is incredible, so checked the code again and found that the driver did
> not reset xdp_tx_in_flight when installing or uninstalling bpf program,
> resulting in xdp_tx_in_flight still retaining the value after the last
> command was run.
> 
> Fixes: c33bfaf91c4c ("net: enetc: set up XDP program under enetc_reconfigure()")
> Cc: stable@...r.kernel.org
> Signed-off-by: Wei Fang <wei.fang@....com>

Reviewed-by: Subbaraya Sundeep <sbhatta@...vell.com>

Thanks,
Sundeep