From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <50D084A7.8080508@siemens.com> Date: Tue, 18 Dec 2012 15:58:47 +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> In-Reply-To: <50D081EB.6080800@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 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. > > 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 ;) Best regards, Wolfgang