On 12/20/2012 05:22 PM, Wolfgang Mauerer wrote:
> On 19/12/12 22:06, Gilles Chanteperdrix wrote:
>> On 12/18/2012 03:58 PM, Wolfgang Mauerer wrote:
>>
>>> On 18/12/12 15:47, Gilles Chanteperdrix wrote:
>>>> On 12/18/2012 12:23 PM, Jan Kiszka wrote:
>>>>> On 2012-12-15 20:16, Gilles Chanteperdrix wrote:
>>>>>> On 12/15/2012 11:03 PM, Wolfgang Mauerer wrote:
>>>>>>
>>>>>>> Hi Gilles,
>>>>>>>
>>>>>>> On 15/12/2012 22:24, Gilles Chanteperdrix wrote:
>>>>>>>
>>>>>>>> I see some (recent) activity on this git repository:
>>>>>>>> https://github.com/siemens/ipipe/commits/core-3.5_for-upstream
>>>>>>>>
>>>>>>>> In what state is this branch, can I pull from it?
>>>>>>> please don't pull yet, I need to port a few more patches forward
>>>>>>> and fix one known issue with the tree. But I'll try to send a
>>>>>>> pull/discussion request next week.
>>>>>>>
>>>>>>>> At least the changes allowing preempt_disable()/preempt_enable() to be
>>>>>>>> called from non-root context look dubious.
>>>>>>> are you referring to 767f0d43fe3? This one still carries a TODO
>>>>>>> item in the description to remind me to check with which
>>>>>>> non-x86 archs this can cause problems, and what we can do about
>>>>>>> them.
>>>>>>
>>>>>>
>>>>>> Actually, we already have ipipe_safe_current(), so I guess what you need
>>>>>> is ipipe_safe_current_thread_info() ?
>>>>>
>>>>> That cannot work unless you patch all the ftrace and perf stack - which
>>>>> would surely not be a good idea /wrt maintainability.
>>>>>
>>>>> The point is remove the instrumentation from preempt_disable/enable at
>>>>> least on those archs that do not need it. And then to look at the archs
>>>>> that still have stack-based thread_info, if we cannot change this, at
>>>>> least for CONFIG_IPIPE enabled.
>>> are you talking about moving the arch's thread_info away from the stack
>>> to some per-processor area like x86's PDA? At a first glance, that
>>> sounds more invasive than changing preempt_xyz() in perf and ftrace
>>> to me, especially since the changes to perf/ftrace should be fairly
>>> straightforward -- just replace calls to preempt_xyz with calls
>>> to preempt_xyz_save() based on ipipe_safe_current_thread_info().
>>>
>>> The easiest thing is to simply say that perf and ftrace are not
>>> supported on archs that cannot reliably read thread_info from non-root
>>> context, but that does not seem very attractive to me.
>>
>>
>> What I am talking about is:
>> - defining preempt_disable/preempt_enable to be
>> ipipe_safe_preempt_disable/ipipe_safe_preempt_enable when CONFIG_FTRACE
>> or CONFIG_PERF is on
>> - for x86_64 (because even on x86_32, preempt_enable/disable use the
>> stack pointer) definee ipipe_safe_preempt_disable/enable to be normal
>> versions
>>
>> Now, if you think the implementation of
>> ipipe_safe_preempt_disable/enable I propose for non x86 architectures is
>> not what should be done, then do not define anything and generate a
>> #error when ipipe_safe_preempt_disable/enable are not defined (and
>> ftrace or perf are on).
> no, your proposal is quite fine. But I guess it would be advantageous
> if we could keep the root-only checks in all preempt code except
> when employed for ftrace and perf. This can be done by
> exchanging the preempt_xyz() calls in the appropriate files to the
> variants based on ipipe_safe_*(), and leave the rest unmodified.
> How's that sound? I'm trying to finish the patch soon, but there are
> unfortunately lots of other commitments towards the end of the year.
>From what I understood from Jan answer, we want to avoid that for ease
of maintenance.
>
>>
>>>>
>>>> The problem is the "then", we can not stay with a solution which works
>>>> only for x86_64. The current contents of the github tree which disables
>>>> the ipipe_root_context check on all architectures can not be merged as is.
>>>
>>> sure, the tree cannot be merged as is. That's why I asked for some more
>>> time ;)
> >
>> The thing is, I would like to release before next week-end... I know I
>> have waited many monthes, but this has to take place at some point...
>
> oh, sorry, I was not aware of a release deadline. Knowing it would have
> been beneficial for the planning... But if you want to release soon,
> then how about just dropping support for ftrace and perf? I can prepare
> a corresponding tree for this scenario if you like.
It would be great, thanks.
--
Gilles.
_______________________________________________
Xenomai mailing list
[email protected]
http://www.xenomai.org/mailman/listinfo/xenomai
