linux-kernel - Re: [PATCH net-next] net: dev: introduce netdev_drop

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Date:   Wed, 09 Feb 2022 02:20:07 +0000
From:   yajun.deng@...ux.dev
To:     "Jakub Kicinski" <kuba@...nel.org>
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()

February 9, 2022 8:27 AM, "Jakub Kicinski" <kuba@...nel.org> wrote:

> On Tue, 8 Feb 2022 14:43:18 +0800 Yajun Deng wrote:
> 
>> We will use 'sudo perf record -g -a -e skb:kfree_skb' command to trace
>> the dropped packets when dropped increase in the output of ifconfig.
>> But there are two cases, one is only called kfree_skb(), another is
>> increasing the dropped and called kfree_skb(). The latter is what
>> we need. So we need to separate these two cases.
>> 
>> From the other side, the dropped packet came from the core network and
>> the driver, we also need to separate these two cases.
>> 
>> Add netdev_drop_inc() and add a tracepoint for the core network dropped
>> packets. use 'sudo perf record -g -a -e net:netdev_drop' and 'sudo perf
>> script' will recored the dropped packets by the core network.
>> 
>> Signed-off-by: Yajun Deng <yajun.deng@...ux.dev>
> 
> Have you seen the work that's being done around kfree_skb_reason()?

Yes, I saw it. The focus of kfree_skb_reason() is trace kfree_skb() and the reason, 
but the focus of this patch only traces this case of the dropped packet.

I don't want to trace all kfree_skb(), but I just want to trace the dropped packet.

This command 'sudo perf record -g -a -e skb:kfree_skb' would trace all kfree_skb(),
kfree_skb() would drowned out the case of dropped packets when the samples were too large.