netdev - Re: [PATCH net-next] net: dev: introduce netdev_drop

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Date:   Wed, 9 Feb 2022 07:31:08 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     yajun.deng@...ux.dev
Cc:     davem@...emloft.net, rostedt@...dmis.org, mingo@...hat.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: dev: introduce netdev_drop_inc()

On Wed, 09 Feb 2022 07:27:44 +0000 yajun.deng@...ux.dev wrote:
> February 9, 2022 11:53 AM, "Jakub Kicinski" <kuba@...nel.org> wrote:
> > IIRC perf support filters, I think with -f? We can't add a tracepoint
> > for every combination of attributes.  
> 
> Yes, we can use a command like this: " sudo perf record -g -a -e skb:kfree_skb --filter 'protocol == 0x0800' ",
> However, only the filter is defined in kfree_skb tracepoint are available.
> 
> The purpose of this patch is record {rx_dropped, tx_dropped, rx_nohandler} in struct net_device, to distinguish 
> with struct net_device_stats. 
> 
> We don't have any tracepoint records {rx_dropped, tx_dropped, rx_nohandler} in struct net_device now. 
> Can we add {rx_dropped, tx_dropped, rx_nohandler} in kfree_skb tracepoint?  like this:
> 
>         TP_STRUCT__entry(
>                 __field(void *,         skbaddr)
>                 __field(void *,         location)
>                 __field(unsigned short, protocol)
>                 __field(enum skb_drop_reason,   reason)
>                 __field(unsigned long,  rx_dropped)
>                 __field(unsigned long,  tx_dropped)
>                 __field(unsigned long,  rx_nohandler)
> 
>         ),
> 
>         TP_fast_assign(
>                 __entry->skbaddr = skb;
>                 __entry->location = location;
>                 __entry->protocol = ntohs(skb->protocol);
>                 __entry->reason = reason;
>                 __entry->rx_dropped   = (unsigned long)atomic_long_read(&skb->dev->rx_dropped);
>                 __entry->tx_dropped   = (unsigned long)atomic_long_read(&skb->dev->tx_dropped);
>                 __entry->rx_nohandler = (unsigned long)atomic_long_read(&skb->dev->rx_nohandler);
>         ),
> 
> If so, we can record this but not add a tracepoint.

You can use bpftrace to dereference extra information.