>>My question concerns the following patch which was incorporated into the >>2.6.22 kernel (quoted from that change log): ... "futex priority based wakeup" >>After updating to this version of the kernel, I was able to observe the >>above fix, where multiple RT threads invoking pthread_cond_wait(), and the >>highest priority thread will acquire the mutex first, after the thread >>holding the mutex calls pthread_cond_signal(); pthread_mutex_unlock()
>>However, since kernel 2.6.23, it seems that the functionality relating to >>this "priority based wakeup" has disappeared. >>I understand there have been significant changes in this kernel concerning >>the "Completely Fair Scheduler" replacing the "mainline" scheduler; >>however my understanding is that the RT functionality would be preserved. >>This does not appear to be the case based on repeating the experiment >>described above. >Hi, > I am not sure if this is whats happening to you (*), but there is a >known problem in the mainline tree related to the system allowing lower >priority threads to stay on the CPU under certain circumstances. > >You can see the problem happening with the following test: > >http://rt.wiki.kernel.org/index.php/Preemption_Test > >and I know the problem goes back to at least 2.6.16. > >Steven Rostedt and I submitted some patches to address the issue, and >they have been accepted into Ingo's sched-devel tree. I would suggest >trying your code against Ingo's tree and see if the problem persists. >You can get it from: > >git://git.kernel.org/pub/scm/linux/kernel/git/mingo/linux-2.6-sched->de vel.git Thanks for the suggestion, however I've just tried this kernel, but the pthread_cond_wait() behaviour still remains as per 2.6.23 described above (i.e. highest prio thread doesnt get woken first). >>(*) I have no information on whether the futex-plist implemetation was >>pulled from the tree to cause your regression. I've just had a look at the code from the 2.6.24 kernel and it seems as though the futex priority list patch code is still included. >>It is possible that the changes between 22 and 23 are just tickling >>your environment enough to bring out this RT-preempt issue. Or that the changes between 22 and 23 are bringing out another issue whereby the desired behaviour of futex-plist is somehow being circumvented. If so, my questions still stand to anyone who might know what has caused the change in pthread_cond_wait() behaviour for RT threads between the 22 and 23 kernels. Cheers, Mark -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
