From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next] trace_events_filter: conditional trace event
 (tcp_probe full=0)
Date: Mon, 12 Feb 2018 11:32:15 -0500 (EST)
Message-ID: <20180212.113215.529432620125895990.davem@davemloft.net>
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Cc: mislam4@kent.edu, tom.zanussi@linux.intel.com,
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        stephen@networkplumber.org, mathieu.desnoyers@polymtl.ca,
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From: Masami Hiramatsu <mhiramat@kernel.org>
Date: Tue, 13 Feb 2018 01:29:03 +0900

> On Mon, 12 Feb 2018 00:08:46 -0500
> "Md. Islam" <mislam4@kent.edu> wrote:
> 
>> Recently tcp_probe kernel module has been replaced by trace_event. Old
>> tcp_probe had full=0 option where it only takes a snapshot only when
>> congestion window is changed. However I did not find such
>> functionality in trace_event.
> 
> Yes, that seems broken to me. You should filter by using perf script or
> bpf. I'm not so clear about network stack, but it seems that cwnd can be
> set for each tcp connection. This means "current snd_cwnd" must be stored
> for each connection.

'bpf' is definitely the way to do custom stateful things like this.