linux-kernel - Re: [PATCH v1 5/5] idpf: warn on possible ctlq overflow

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Message-ID: <66bbb1db36a9c_8a56a29485@willemb.c.googlers.com.notmuch>
Date: Tue, 13 Aug 2024 15:19:55 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Manoj Vishwanathan <manojvishy@...gle.com>, 
 Tony Nguyen <anthony.l.nguyen@...el.com>, 
 Przemek Kitszel <przemyslaw.kitszel@...el.com>, 
 "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 intel-wired-lan@...ts.osuosl.org
Cc: netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 google-lan-reviews@...glegroups.com, 
 Willem de Bruijn <willemb@...gle.com>, 
 Manoj Vishwanathan <manojvishy@...gle.com>
Subject: Re: [PATCH v1 5/5] idpf: warn on possible ctlq overflow

Manoj Vishwanathan wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> The virtchannel control queue is lossy to avoid deadlock. Ensure that
> no losses occur in practice. Detect a full queue, when overflows may
> have happened.
> 
> In practice, virtchnl is synchronous currenty and messages generally
> take a single slot. Using up anywhere near the full ring is not
> expected.
> 
> Tested: Running several traffic tests and no logs seen in the dmesg
> 
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

This was an internal patch. Not really intended for upstream as is.

> Signed-off-by: Manoj Vishwanathan <manojvishy@...gle.com>
> ---
>  drivers/net/ethernet/intel/idpf/idpf_virtchnl.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> index 07239afb285e..1852836d81e4 100644
> --- a/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> +++ b/drivers/net/ethernet/intel/idpf/idpf_virtchnl.c
> @@ -218,6 +218,15 @@ static int idpf_mb_clean(struct idpf_adapter *adapter)
>  	if (err)
>  		goto err_kfree;
>  
> +	/* Warn if messages may have been dropped */
> +	if (num_q_msg == IDPF_DFLT_MBX_Q_LEN) {
> +		static atomic_t mbx_full = ATOMIC_INIT(0);
> +		int cnt;
> +
> +		cnt = atomic_inc_return(&mbx_full);
> +		net_warn_ratelimited("%s: ctlq full (%d)\n", __func__, cnt);

A single static variable across all devices.

If this indeed should never happen, a WARN_ON_ONCE will suffice.