linux-kernel - Re: [PATCH v7 6/8] drm_print: instrument drm_debug

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Date:   Sun, 5 Sep 2021 12:50:48 -0600
From:   jim.cromie@...il.com
To:     Jason Baron <jbaron@...mai.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        amd-gfx mailing list <amd-gfx@...ts.freedesktop.org>,
        intel-gvt-dev@...ts.freedesktop.org,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>
Subject: Re: [PATCH v7 6/8] drm_print: instrument drm_debug_enabled

On Tue, Aug 31, 2021 at 2:21 PM Jim Cromie <jim.cromie@...il.com> wrote:
>
> Duplicate drm_debug_enabled() code into both "basic" and "dyndbg"
> ifdef branches.  Then add a pr_debug("todo: ...") into the "dyndbg"
> branch.
>
> Then convert the "dyndbg" branch's code to a macro, so that its
> pr_debug() get its callsite info from the invoking function, instead
> of from drm_debug_enabled() itself.
>
> This gives us unique callsite info for the 8 remaining users of
> drm_debug_enabled(), and lets us enable them individually to see how
> much logging traffic they generate.  The oft-visited callsites can
> then be reviewed for runtime cost and possible optimizations.
>
> Heres what we get:
>
> bash-5.1# modprobe drm
> dyndbg: 384 debug prints in module drm
> bash-5.1# grep todo: /proc/dynamic_debug/control
> drivers/gpu/drm/drm_edid.c:1843 [drm]connector_bad_edid =_ "todo: maybe avoid via dyndbg\012"
> drivers/gpu/drm/drm_print.c:309 [drm]___drm_dbg =p "todo: maybe avoid via dyndbg\012"
> drivers/gpu/drm/drm_print.c:286 [drm]__drm_dev_dbg =p "todo: maybe avoid via dyndbg\012"
> drivers/gpu/drm/drm_vblank.c:1491 [drm]drm_vblank_restore =_ "todo: maybe avoid via dyndbg\012"
> drivers/gpu/drm/drm_vblank.c:787 [drm]drm_crtc_vblank_helper_get_vblank_timestamp_internal =_ "todo: maybe avoid via dyndbg\012"
> drivers/gpu/drm/drm_vblank.c:410 [drm]drm_crtc_accurate_vblank_count =_ "todo: maybe avoid via dyndbg\012"
> drivers/gpu/drm/drm_atomic_uapi.c:1457 [drm]drm_mode_atomic_ioctl =_ "todo: maybe avoid via dyndbg\012"
> drivers/gpu/drm/drm_edid_load.c:178 [drm]edid_load =_ "todo: maybe avoid via dyndbg\012"
>
> At quick glance, edid won't qualify, drm_print might, drm_vblank is
> strongest chance, maybe atomic-ioctl too.
>
> Signed-off-by: Jim Cromie <jim.cromie@...il.com>
> ---

heres 120 seconds of enabled todos, from this patch

[jimc@...do wk-next]$ journalctl -b0 | grep todo | grep 'frodo kernel'
[jimc@...do wk-next]$ sudo su -c 'echo format ^todo: +pfml >
/proc/dynamic_debug/control;  sleep 120; echo format ^todo: -p >
/proc/dynamic_debug/control'
[sudo] password for jimc:
[jimc@...do wk-next]$ journalctl -b0 | grep todo | grep 'frodo kernel'
 > todo-120-log
[jimc@...do wk-next]$ wc todo-120-log
  228  2516 24066 todo-120-log

so overall thats not too much work, not so many bitchecks as to be
worth avoiding.

I think I'll try hitting it with my new igt-tools hammer, see what breaks :-)


[jimc@...do wk-next]$ hsto todo-120-log
120 :  drm:drm_crtc_vblank_helper_get_vblank_timestamp_internal:787:
todo: maybe avoid via dyndbg
40 :  i915:process_csb:1904: todo: maybe avoid via dyndbg
20 :  drm:drm_vblank_restore:1491: todo: maybe avoid via dyndbg
20 :  drm:drm_crtc_accurate_vblank_count:410: todo: maybe avoid via dyndbg
20 :  i915:skl_print_wm_changes:6068: todo: maybe avoid via dyndbg
2 :  dyndbg: applied: func="" file="" module="" format="^todo:" lineno=0-0
2 :  dyndbg: parsed: func="" file="" module="" format="^todo:" lineno=0-0
1 :  dyndbg: split into words: "format" "^todo:" "-p"
1 :  dyndbg: split into words: "format" "^todo:" "+pfml"
1 :  dyndbg: query 0: "format ^todo: -p" mod:*
1 :  dyndbg: query 0: "format ^todo: +pfml" mod:*