lkml.org 
[lkml]   [2018]   [May]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCHv2][SMB3] Add kernel trace support
On Sat, May 19, 2018 at 6:22 PM, Dave Chinner <david@fromorbit.com> wrote:
> On Fri, May 18, 2018 at 01:43:14PM -0700, Steve French wrote:
>> On Fri, May 18, 2018 at 11:46 AM, Ralph Böhme <slow@samba.org> wrote:
>> > On Thu, May 17, 2018 at 09:36:36PM -0500, Steve French via samba-technical wrote:
>> >> Patch updated with additional tracepoint locations and some formatting
>> >> improvements. There are some obvious additional tracepoints that could
>> >> be added, but this should be a reasonable group to start with.
>> >>
>> >> From edc02d6f9dc24963d510c7ef59067428d3b082d3 Mon Sep 17 00:00:00 2001
>> >> From: Steve French <stfrench@microsoft.com>
>> >> Date: Thu, 17 May 2018 21:16:55 -0500
>> >> Subject: [PATCH] smb3: Add ftrace tracepoints for improved SMB3 debugging
>> >>
>> >> Although dmesg logs and wireshark network traces can be
>> >> helpful, being able to dynamically enable/disable tracepoints
>> >> (in this case via the kernel ftrace mechanism) can also be
>> >> helpful in more quickly debugging problems, and more
>> >> selectively tracing the events related to the bug report.
>> >>
>> >> This patch adds 12 ftrace tracepoints to cifs.ko for SMB3 events
>> >> in some obvious locations. Subsequent patches will add more
>> >> as needed.
>> >>
>> >> Example use:
>> >> trace-cmd record -e cifs
>> >> <run test case>
>> >> trace-cmd show
>> >
>> > pardon my ignorance, but are these tracepoints usable with other tracing
>> > frameworks like Systemtap?
>> >
>> > Last time I checked, Systemtap looked like *the* tool.
>
> Systemtap is great when you have a need for custom tracing. But for
> day-to-day kernel development, tracepoints are far more useful
> because they are always there and can cover all the common
> situations that you need to trace.
>
> And when it comes to debugging a one-off user problem when the user
> knows nothing about systemtap? Nothing beats asking the user
> to run a trace on built-in tracepoints, reproduce the problem and
> send the trace report back as per the above example.

Yep - it has already been helpful in debugging problems.

Main problem I hit using the new tracepoints over the past few days
was entries being discarded from the buffer - I had a counter leak (now
fixed) that xfstest showed ... but about 90% of the entries were dropped.
Tried increasing buffer size but might have made things worse not better.
Ideas how to force more entries to be saved?

>> > Is there a generic trace
>> > point infrastructure that tracing tools can consume, so we're not tied to
>> > ftrace?
>>
>> At the kernel filesystem/mm summit a few recommended using ftrace
>> (trace-cmd). Don't know what
>> the thinking is about this vs. systemtap these days. There was a nice
>> three part series
>> describing ftrace/trace-cmd on lwn
>> (https://old.lwn.net/Articles/365835/) a while ago.
>>
>> In terms of useability "trace-cmd" looked good to me and much more
>> powerful than the
>> current dmesg based printk style debugging.
>
> And then you learn about trace_printk() for putting custom one-off
> debug into the tracepoint stream and wonder why you didn't know
> about this years ago :P

Thanks for the pointers at the summit ...



--
Thanks,

Steve

\
 
 \ /
  Last update: 2018-05-20 03:57    [W:0.072 / U:9.172 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site