linux-kernel - Re: [PATCH 0/2] Add SCMI full message tracing

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Date:   Wed, 29 Jun 2022 19:19:32 +0100
From:   Cristian Marussi <cristian.marussi@....com>
To:     Jim Quinlan <james.quinlan@...adcom.com>
Cc:     open list <linux-kernel@...r.kernel.org>,
        "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Lukasz Luba <lukasz.luba@....com>
Subject: Re: [PATCH 0/2] Add SCMI full message tracing

On Mon, Jun 27, 2022 at 03:05:57PM -0400, Jim Quinlan wrote:
> On Thu, Jun 23, 2022 at 10:55 AM Cristian Marussi
> <cristian.marussi@....com> wrote:
> >
> > Hi,
> >
> > after a few recent troubles handling too strictly out-of-spec replies from
> > SCMI servers deployed in the wild, I though it could have been useful to
> > have a basic way to dump at will the effective full payloads of successfuly
> > transmitted/received SCMI messages.
> >
> > The existing SCMI traces already collect a bunch of information about SCMI
> > message exchanges but they do NOT keep any payload information: this is
> > certainly preferable most of the time since dumping full SCMI messages to
> > the trace buffer involves a full copy of the payload.
> >
> > For this reason I added a new distinct trace_scmi_msg_dump with this series
> > in order to be able to selectively enable at will message dumping only when
> > required.
> >
> > Only successfully transmitted and received (valid) xfers are dumped.
> >
> > At first I was thinking about just dumping raw header and payload, but in
> > order to make the log a bit more human readable (without the need of
> > tooling to parse the log), I added some parsing/interpretation of the
> > header, so that the final result is something like:
> >
> > root@...-guest:~# echo 1 > /sys/kernel/debug/tracing/events/scmi/scmi_msg_dump/enable
> > root@...-guest:~# cat /sys/kernel/debug/tracing/trace_pipe
> >
> > (my annotations non on traces =>>)                       proto  type  cmd   seq  status    payload
> >                                                           |      |    |      |     |        |
> >  ++ cmd/reply                                             |      |    |      |     |        |
> >    cat-224     [002] .....   147.755847: scmi_msg_dump: [0x15]:CMND:[0x06]:[0021]:[0]: 0000000000000000
> > <idle>-0       [000] d.h2.   147.758311: scmi_msg_dump: [0x15]:RESP:[0x06]:[0021]:[0]: 25000000000000000000000000000000
> >I'll probably still use a script, but
> as you are keep
> >
> >  ++ cmd/reply/delayed
> >    cat-223     [001] .....   122.384192: scmi_msg_dump: [0x15]:CMND:[0x06]:[0020]:[0]: 0100000001000000
> > <idle>-0       [000] d.h2.   122.405548: scmi_msg_dump: [0x15]:RESP:[0x06]:[0020]:[0]:
> > <idle>-0       [000] d.h2.   122.425839: scmi_msg_dump: [0x15]:DLYD:[0x06]:[0020]:[0]: 01000000a05a320000000000efbeaddefecafeca
> >
> >
> >  ++ enable notif/notif
> > iio_generic_buf-233     [003] .....   522.399690: scmi_msg_dump: [0x15]:CMND:[0x0A]:[0024]:[0]: 0800000003000000
> >          <idle>-0       [000] dNh2.   522.417778: scmi_msg_dump: [0x15]:RESP:[0x0A]:[0024]:[0]: 00000000
> >          <idle>-0       [000] d.h2.   522.500945: scmi_msg_dump: [0x15]:NOTI:[0x01]:[0000]:[0]: 000000000800000008daffffffffffff0040d3a45d46fb1610daffffffffffff0040d3a45d46fb1618daffffffffffff0040d3a45d46fb16
> >
> > Payload is dumped as it comes through byte-by-byte without any endianity
> > conversion to avoid further load on the system.
> >
> > Any thoughs ?
> 
> Hi Christian,
> I haven't tested this but the format looks good to me.  I have a
> couple of minor suggestions
> below.
> 

Hi Jim,

thanks for having a look.

> As all numbers are hex, consider dropping the '0x'.  BTW,  the seq
> value (eg [0020]) is hex but does not have '0x'.
> 

Yes indeed, good point.

> Some TP_printk()s use this  style:
> 
>         scmi_msg_dump: pt=15 t=CMND cmd=06 seq=0021 s=0 pyld=12345678abcdef
> 
> which allows one to easily grep, for example, for all non-zero returns
> 
>         grep 's=[^0]'
> 
> This format is also easy to parse with a script:  strip the preamble,
> split on whitespace, and then split on '=' to get the  [key, value]
> pairs.

In fact having a grep-friendly format is better.

Thanks for your feedback, I'll wait to see if someone else wants to
chime in and repost.

Thanks,
Cristian