linux-kernel - Re: [PATCH v8 2/2] mctp pcc: Implement MCTP over PCC Transport

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Message-ID: <1e7bacaf-3dee-4c95-9618-07b1dd253509@amperemail.onmicrosoft.com>
Date: Mon, 16 Dec 2024 17:29:13 -0500
From: Adam Young <admiyo@...eremail.onmicrosoft.com>
To: Joe Damato <jdamato@...tly.com>, admiyo@...amperecomputing.com,
 Jeremy Kerr <jk@...econstruct.com.au>,
 Matt Johnston <matt@...econstruct.com.au>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
 Sudeep Holla <sudeep.holla@....com>,
 Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Huisong Li <lihuisong@...wei.com>
Subject: Re: [PATCH v8 2/2] mctp pcc: Implement MCTP over PCC Transport

After looking in to the helper functions that Jeremy suggested, I cannot 
say for certain if there is a way to record the length errors using 
those function.

On 11/21/24 13:49, Joe Damato wrote:
>> +static void mctp_pcc_client_rx_callback(struct mbox_client *c, void *buffer)
>> +{
>> +	struct mctp_pcc_ndev *mctp_pcc_dev;
>> +	struct mctp_pcc_hdr mctp_pcc_hdr;
>> +	struct mctp_skb_cb *cb;
>> +	struct sk_buff *skb;
>> +	void *skb_buf;
>> +	u32 data_len;
>> +
>> +	mctp_pcc_dev = container_of(c, struct mctp_pcc_ndev, inbox.client);
>> +	memcpy_fromio(&mctp_pcc_hdr, mctp_pcc_dev->inbox.chan->shmem,
>> +		      sizeof(struct mctp_pcc_hdr));
>> +	data_len = mctp_pcc_hdr.length + MCTP_HEADER_LENGTH;
>> +
>> +	if (data_len > mctp_pcc_dev->mdev.dev->mtu) {
>> +		mctp_pcc_dev->mdev.dev->stats.rx_dropped++;
> I'm not an expert on rtnl stats, but maybe this should be
> accounted for as rx_length_errors ?
>
> And when rx_dropped is accounted in the stats callback it can add
> rx_length_errors in as well as setting rtnl_link_stats64's
> rx_length_errors?
>
> You've probably read this already, but just in case:
>
> https://docs.kernel.org/networking/statistics.html#struct-rtnl-link-stats64

The code will end up looking like this instead:

         dstats = this_cpu_ptr(mctp_pcc_ndev->mdev.dev->dstats);
         u64_stats_update_begin(&dstats->syncp);
         if (data_len > mctp_pcc_ndev->mdev.dev->mtu) {
                 u64_stats_inc(&dstats->rx_drops);
                 u64_stats_inc(&dstats->rx_drops);
                 u64_stats_update_end(&dstats->syncp);
                 return;
         }
         if (!skb) {
                 u64_stats_inc(&dstats->rx_drops);
                 u64_stats_update_end(&dstats->syncp);
                 return;
         }
         u64_stats_inc(&dstats->rx_packets);
         u64_stats_add(&dstats->rx_bytes, data_len);
         u64_stats_update_end(&dstats->syncp);

And the stats function gets dropped from

static const struct net_device_ops mctp_pcc_netdev_ops = {
         .ndo_start_xmit = mctp_pcc_tx,
};

So I think it is either/or using the heplers or setting the length 
error.  I am leaning toward using the helper functions.