From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4A0BD3EE.2@domain.hid> Date: Thu, 14 May 2009 10:18:54 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <4A0AC1C8.4050006@domain.hid> <4A0AC3F9.9090103@domain.hid> <4A0AC8A6.1000701@domain.hid> <4A0AE2AC.7010302@domain.hid> <4A0AE9EF.1010107@domain.hid> <4A0B34BF.3020707@domain.hid> In-Reply-To: <4A0B34BF.3020707@domain.hid> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] Troubles with switchtest List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gilles Chanteperdrix Cc: xenomai-core Gilles Chanteperdrix wrote: > Jan Kiszka wrote: >> Gilles Chanteperdrix wrote: >>> Jan Kiszka wrote: >>>> Gilles Chanteperdrix wrote: >>>>> Jan Kiszka wrote: >>>>>> Hi Gilles, >>>>>> >>>>>> I'm currently facing a nasty effect with switchtest over latest git head >>>>>> (only tested this so far): running it inside my test VM (ie. with >>>>>> frequent excessive latencies) I get a stalled Linux timer IRQ quite >>>>>> quickly. System is otherwise still responsive, Xenomai timers are still >>>>>> being delivered, other Linux IRQs too. switchtest complained about >>>>>> >>>>>> "Warning: Linux is compiled to use FPU in kernel-space." >>>>>> >>>>>> when it was started. Kernels are 2.6.28.9/ipipe-x86-2.2-07 and >>>>>> 2.6.29.3/ipipe-x86-2.3-01 (LTTng patched in, but unused), both show the >>>>>> same effect. >>>>>> >>>>>> Seen this before? >>>>> The warning about Linux being compiled to use FPU in kernel-space means >>>>> that you enabled soft RAID or compiled for K7, Geode, or any other >>>> RAID is on (ordinary server config). >>> By the way, I wonder how MMX accelerated software raid works on K7, >>> since the way I understand the code, calls to kernel_fpu_begin() can not >>> be nested. >>> >>> If you think they can be nested, then we can make switchtest test fpu in >>> Linux kernel-space when these options are enabled. >> Sorry, I haven't looked that close into the in-kernel FPU handling so >> far. What users are nested in the standard kernel? Or is it RAID in itself? > > RAID uses FPU. And on K7, basic things like clearing or copying user > pages, or even large memcpy do use FPU too. So, I would expect that when > enabling both, they could happen to be nested. > I think the trick against /this/ is preempt_disable/enable in kernel_fpu/begin/end. But that won't work for Xenomai, of course. Jan -- Siemens AG, Corporate Technology, CT SE 2 Corporate Competence Center Embedded Linux