linux-kernel - Re: [RFC PATCH v3 0/5] tracing: common error

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Date:   Wed, 13 Mar 2019 09:09:33 -0500
From:   Tom Zanussi <zanussi@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     rostedt@...dmis.org, tglx@...utronix.de, namhyung@...nel.org,
        bigeasy@...utronix.de, joel@...lfernandes.org,
        linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Subject: Re: [RFC PATCH v3 0/5] tracing: common error_log for ftrace

Hi Masami,

On Wed, 2019-03-13 at 22:03 +0900, Masami Hiramatsu wrote:
> On Tue, 12 Mar 2019 11:49:11 -0500
> Tom Zanussi <zanussi@...nel.org> wrote:
> 
> > Hi Masami,
> > 
> > On Tue, 2019-03-12 at 15:26 +0900, Masami Hiramatsu wrote:
> > > Hi Tom,
> > > 
> > > On Tue, 5 Mar 2019 23:06:46 +0900
> > > Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > > 
> > > > On Mon,  4 Mar 2019 17:36:43 -0600
> > > > > Changes from v2:
> > > > > 
> > > > >   - Added [n] numbering as suggested by Masami
> > > 
> > > Hmm, this seems a bit different what I suggested.
> > > 
> > > I'm trying to port probe event's error report on
> > > your error log, and I found that the number is
> > > just shifted as below.
> > > 
> > > When I filled the log with errors.
> > > =============
> > > /sys/kernel/debug/tracing # cat error_log 
> > > [1] trace_kprobe: error: Invalid unsigned integer string
> > >   Command: r10aa00:foo/bar vfs
> > >             ^
> > > ...
> > > 
> > > [7] trace_kprobe: error: Group name must follow C naming
> > > convention
> > >   Command: p:a-b/bar vfs_read
> > >              ^
> > > [8] trace_kprobe: error: Event name is too long
> > >   Command:
> > > p:a/barrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
> > > rrrr
> > > rrrrrrrrrrr vfs_read
> > > =============
> > > 
> > > And do one more error, 
> > > 
> > > =============
> > > /sys/kernel/debug/tracing # cat error_log 
> > > [1] trace_kprobe: error: Maxactive is too big
> > >   Command: r0xaa00:foo/bar vfs
> > > 
> > > ....
> > > 
> > > [7] trace_kprobe: error: Event name is too long
> > >   Command:
> > > p:a/barrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr
> > > rrrr
> > > rrrrrrrrrrr vfs_read
> > >                ^
> > > [8] trace_kprobe: error: Event name must follow C naming
> > > convention
> > >   Command: p:a/bar.c vfs_read
> > >                ^
> > > =============
> > > 
> > > The number of logs are changed :(  This can confuse users.
> > > I think it is better to keep the number as a unique number for
> > > each entry as below.
> > > 
> > 
> > Hmm, that makes sense, but I wonder if that will also confuse
> > users,
> > when the log wraps around and no longer starts at [1] and there's
> > no
> > way to retrieve the previous errors.
> 
> It is OK, that is same as dmesg. If user needs to keep watching it,
> it should be dumped to disk by a daemon.
> 
> > 
> > I took your suggestion as a way mainly to clearly delineate each
> > error,
> > since without the [number] or something similar, they all kind of
> > run
> > together.
> > 
> > Not sure what advantage numbering itself provides - would some
> > other
> > non-numbered separator work?
> 
> What about timestamp, similar to dmesg?
> 

Yeah, I think that makes more sense - unlike the counter, there's no
sense that you may be missing some prior messages.

Thanks,

Tom 

> Thank you,
> 
> 
>