From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <50D22C63.6060800@xenomai.org> Date: Wed, 19 Dec 2012 22:06:43 +0100 From: Gilles Chanteperdrix 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> In-Reply-To: <50D084A7.8080508@siemens.com> Content-Type: text/plain; charset=UTF-8 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: Wolfgang Mauerer Cc: Wolfgang Mauerer , Jan Kiszka , "xenomai@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.