From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <50D33B52.6010301@siemens.com> Date: Thu, 20 Dec 2012 17:22:42 +0100 From: Wolfgang Mauerer MIME-Version: 1.0 References: <50CCEA7E.1080000__518.307140055363$1355606686$gmane$org@xenomai.org> <50CCF3B8.5000201@linux-kernel.net> <50CCF6C4.80408@xenomai.org> <50D05218.1080406@web.de> <50D081EB.6080800@xenomai.org> <50D084A7.8080508@siemens.com> <50D22C63.6060800@xenomai.org> In-Reply-To: <50D22C63.6060800@xenomai.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] core-3.5 for x86 List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: Wolfgang Mauerer , Jan Kiszka , "xenomai@xenomai.org" 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. > >>> >>> 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. Best regards, Wolfgang