netdev - Re: [PATCH net-next] sctp: move trace_sctp_probe_path into sctp_outq

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Message-ID: <20191227022801.GI5058@localhost.localdomain>
Date:   Thu, 26 Dec 2019 23:28:01 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     qdkevin.kou@...il.com, netdev@...r.kernel.org,
        nhorman@...driver.com, linux-sctp@...r.kernel.org
Subject: Re: [PATCH net-next] sctp: move trace_sctp_probe_path into
 sctp_outq_sack

On Thu, Dec 26, 2019 at 03:38:35PM -0800, David Miller wrote:
> From: Kevin Kou <qdkevin.kou@...il.com>
> Date: Fri, 27 Dec 2019 07:09:07 +0800
> 
> > 
> > 
> >>From: Kevin Kou <qdkevin.kou@...xxxxxx>
> >>Date: Thu, 26 Dec 2019 12:29:17 +0000
> >>
> >>> This patch is to remove trace_sctp_probe_path from the TP_fast_assign
> >>> part of TRACE_EVENT(sctp_probe) to avoid the nest of entry function,
> >>> and trigger sctp_probe_path_trace in sctp_outq_sack.
> >> ...
> >>
> >>Applied, but why did you remove the trace enabled check, just out of
> >>curiosity?
> > 
> > Actually, the check in trace_sctp_probe_path_enabled also done in
> > trace_sctp_probe_path according to the Macro definition, both check
> > if (static_key_false(&__tracepoint_##name.key)).
> 
> Indeed, thanks for the explanation.

It was duplicated, yes, but it was also a small optimization:

if (enabled) {
  for (X times) {
    if (enabled) {
    }
  }
}

So it wouldn't traverse the list if not needed.  But X is usually 1 or
2 and this list is already traversed multiple times in this code path.