Re: [Xenomai] core-3.5 for x86

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

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).

>>
>> 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...

-- 
                                                                Gilles.