On Tue, Feb 09, 2010 at 09:32:30AM -0000, Leggo, Adam (UK) wrote: | Hello, | | What is the best way of converting an existing device driver to work | under a real-time kernel? | | A device driver provided for a special serial card (Curtiss Wright SL240 | sFDFP card http://www.cwcembedded.com/products/0/1/461.html) works under | vanilla Linux (SLES SP10 SP2 kernel 2.6.16.60-0.21-smp), but compiling | the driver under the real time kernel (2.6.22.19-0.14-rt) the system | locks up and crashes. The rt kernel is being used to write large amounts | of data from the serial card to disk and testing has found the rt kernel | has the best consistent write performance. | | I have gone back to the supplier and they are not interested in | developing a real time version of the driver. So I am trying to modify | the driver myself. The driver code can be provided if anyone wants a | look (released under GPLv2). The oops or panic messages issued when the kernel locks up are a good starting point to find the underlying issue. Due to the nature of PREEMPT_RT subtle concurrency problems on the driver, that may take a lifetime to appear under upstream Linux, will show up every now and then on RT. I would also put my bets on locking. As regular spinlocks are converted to rtmutexes and can therefore sleep, I would check locking on the driver and eventually convert some of the locks to old-style spinlocks. The naming on the non-sleeping locks varies according to the version of the PREEMPT_RT patch in use. Luis -- [ Luis Claudio R. Goncalves Bass - Gospel - RT ] [ Fingerprint: 4FDD B8C4 3C59 34BD 8BE9 2696 7203 D980 A448 C8F8 ] -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
