Message-ID: <4730EC6D.7040709@us.ibm.com>
Date:	Tue, 06 Nov 2007 14:36:29 -0800
From:	Mike Mason <mmlnx@...ibm.com>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
Cc:	ltt-dev@...fik.org, linux-kernel@...r.kernel.org,
	systemtap@...rces.redhat.com
Subject: Re: [to-be-posted-soon] Multiple handlers per marker

Mathieu Desnoyers wrote:
> * Mike Mason (mmlnx@...ibm.com) wrote:
>> Mathieu Desnoyers wrote:
>>> * Mathieu Desnoyers (compudj@...stal.dyndns.org) wrote:
>>>> * Mathieu Desnoyers (mathieu.desnoyers@...ymtl.ca) wrote:
>>>>> * Mike Mason (mmlnx@...ibm.com) wrote:
>>>>>> Hi Mathieu,
>>>>>>
>>>>>> Are you aware of any working being done to allow multiple handlers to 
>>>>>> be attached to a marker?  Something like what kprobes allows.  I've 
>>>>>> started to look into this and don't want to duplicate efforts.
>>>>>>
>>>>> Nope, but I know we will have to address this.
>>>>>
>>>>> Something along the lines of walking an RCU list of function pointers,
>>>>> calling them.
>>>>>
>>>>> The only downside I see is that we will have to pass a va_list * instead
>>>>> of real va args. The could make the marker site a little bit bigger and
>>>>> will change the probe callback arguments.
>>>>>
>>>>> What do you think about these ideas ?
>>>>>
>>>>> If we can find a way to make the common case (only one probe connected)
>>>>> _ultra_ fast, and yet architecture independent, that would be awesome. A
>>>>> simple call is kind of hard to beat though.. So we may have to think
>>>>> about a design with :
>>>>>
>>>>> - One call at the marker site
>>>>> - if 1 probe is installed :
>>>>>   - If the format string is empty, connect a probe without va args.
>>>>>   - If the format string is not empty, connect a "stage 1" probe that 
>>>>> takes
>>>>>     the va args, starts/ends the va_list and calls _one_ function (let's
>>>>>     call it "stage 2" probe), that takes va_list as parameter.
>>>>> - if more than 1 probe is installed :
>>>>>   - The stage 1 probe creates the va_list and passes it to each function
>>>>>     connected, iterated with an RCU list.
>>>>>
>>>>> What do you think ?
>>>>>
>>>>> Mathieu
>>>>>
>>>> I'm working on an implementation.
>>>>
>>> It's ready for testing. Please grab
>>> http://ltt.polymtl.ca/lttng/patch-2.6.24-rc1-git13-lttng-0.10-pre18.tar.bz2
>>> patch name :
>>> markers-support-multiple-probes.patch
>> This patch alone doesn't apply cleanly at all on 2.6.24-rc1-git14.  Are 
>> there other patches in this series I should apply first?
>>
> 
> Yes, the following ones should suffice :
> 
> # instrumentation menu removal
> add-kconfig-to-arch.patch
> add-arch-supports-oprofile.patch
> add-arch-supports-kprobes.patch
> move-kconfig-instrumentation-to-arch.patch
> #
> kprobes-use-mutex-for-insn-pages.patch
> kprobes-dont-use-kprobes-mutex-in-arch-code.patch
> kprobes-declare-kprobes-mutex-static.patch
> declare-array.patch
> text-edit-lock-architecture-independent-code.patch
> text-edit-lock-alternative-i386-and-x86_64.patch
> text-edit-lock-kprobes-architecture-independent.patch
> text-edit-lock-kprobes-i386.patch
> text-edit-lock-kprobes-x86_64.patch
> text-edit-lock-i386-standardize-debug-rodata.patch
> text-edit-lock-x86_64-standardize-debug-rodata.patch
> #
> immediate-values-architecture-independent-code.patch
> immediate-values-kconfig-embedded.patch
> immediate-values-move-kprobes-i386-restore-interrupt-to-kdebug-h.patch
> add-asm-compat-to-x86.patch
> immediate-values-i386-optimization.patch
> immediate-values-powerpc-optimization.patch
> immediate-values-documentation.patch
> #
> linux-kernel-markers-immediate-values.patch
> #
> markers-support-multiple-probes.patch
> 
> Tell me if you still have rejects.

I applied the above patches to 2.6.24-rc1-git14.  They applied fine with just a few offsets until the last patch, which yielded this result:

patching file include/linux/marker.h
Hunk #5 succeeded at 162 with fuzz 2.
patching file kernel/marker.c
Hunk #14 FAILED at 534.
Hunk #15 FAILED at 587.
Hunk #16 FAILED at 621.
Hunk #17 FAILED at 732.
Hunk #18 FAILED at 769.
Hunk #19 succeeded at 791 (offset 12 lines).
5 out of 19 hunks FAILED -- saving rejects to file kernel/marker.c.rej
patching file kernel/module.c
Hunk #1 succeeded at 1998 (offset -3 lines).
Hunk #2 succeeded at 2608 (offset -37 lines).
Hunk #3 succeeded at 2651 with fuzz 1 (offset -3 lines).
patching file include/linux/module.h
Hunk #1 FAILED at 468.
Hunk #2 succeeded at 572 (offset -2 lines).
1 out of 2 hunks FAILED -- saving rejects to file include/linux/module.h.rej
patching file samples/markers/probe-example.c

Mike

> 
> Mathieu
> 
> 
>> Mike
>>
>>> It still need to go through patchcheck.pl and some polishing, but it
>>> seems to work fine for me with multiple probes (the sample marker,
>>> sample probe and multiple instances of my lttng probes can
>>> connect/disconnect without problem).
>>> Currently, the "connect/disconnect" and "arm/disarm" operations are
>>> separate. However, they could be merged. Any comment/preference on this?
>>> Being separate, a probe provider can wait until the very last moment
>>> before it activates its markers, with a minimalistic impact on the
>>> system, but it is not such a strong argument.
>>> Mathieu
> 
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