On Thu, Oct 15, 2009 at 12:44 AM, Leonidas . <leonidas137@xxxxxxxxx> wrote: > On Wed, Oct 14, 2009 at 7:52 PM, vinit dhatrak <vinit.dhatrak@xxxxxxxxx> wrote: >> On Wed, Oct 14, 2009 at 7:43 PM, vinit dhatrak <vinit.dhatrak@xxxxxxxxx> wrote: >>> On Wed, Oct 14, 2009 at 7:39 PM, Leonidas . <leonidas137@xxxxxxxxx> wrote: >>>> On Wed, Oct 14, 2009 at 6:56 AM, vinit dhatrak <vinit.dhatrak@xxxxxxxxx> wrote: >>>>> On Wed, Oct 14, 2009 at 4:34 PM, Leonidas . <leonidas137@xxxxxxxxx> wrote: >>>>>> On Wed, Oct 14, 2009 at 3:34 AM, Leonidas . <leonidas137@xxxxxxxxx> wrote: >>>>>>> Hi, >>>>>>> >>>>>>> I am running Ubuntu Jaunty currently, with kernel version 2.6.28 kernel. >>>>>>> I was assuming that, all the kernels above 2.6 will have CONFIG_PREEMPT >>>>>>> =1 by default, but my default kernel does not have it set. >>>>>>> >>>>>>> Is that the norm? I can understand certain use cases which might require >>>>>>> the kernel to be non pre-emptible but even a regular desktop distro does >>>>>>> not have it set? Surprising? >>>>>>> >>>>>>> -Leo. >>>>>>> >>>>>> >>>>>> >>>>>> Even the vmware image which I use for development does not have >>>>>> CONFIG_PREEMPT=1. >>>>>> though it says kernel is SMP. >>>>>> >>>>>> #uname -a >>>>>> >>>>>> Linux ubuntu-vm 2.6.27.2 -generic #1 SMP Thu Aug 28 17:20:02 UTC 2008 >>>>>> i686 GNU/Linux >>>>>> >>>>>> -Leo. >>>>>> >>>>>> -- >>>>>> To unsubscribe from this list: send an email with >>>>>> "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx >>>>>> Please read the FAQ at http://kernelnewbies.org/FAQ >>>>>> >>>>>> >>>>> >>>>> Ok so I can see 3 option for setting preemption model while building kernel, >>>>> >>>>> 1) CONFIG_PREEMPT_NONE 2) CONFIG_PREEMPT_VOLUNTARY (default) >>>>> 3) CONFIG_PREEMPT (might be Ubuntu specific because I can not see this >>>>> in vanila kernel) >>>>> >>>>> >>>>> So by default on Ubuntu (Desktop), CONFIG_PREEMPT_VOLUNTARY is >>>>> selected not CONFIG_PREEMPT >>>>> >>>>> The difference between symbol exported by these 2 kernels is, >>>>> >>>>> 1) Ubuntu (CONFIG_PREEMPT_VOLUNTARY) (You can see some symbols by kvm >>>>> also but you can ignore them) >>>>> >>>>> vinitd@pe-lt271:~$ cat /proc/kallsyms | grep preempt >>>>> c0121550 T preempt_notifier_register >>>>> c0121580 T preempt_notifier_unregister >>>>> c012a350 t check_preempt_curr_idle >>>>> c012ab50 t check_preempt_curr_rt >>>>> c012ac50 t check_preempt_wakeup >>>>> c045a8f0 r __ksymtab_preempt_notifier_unregister >>>>> c045a8f8 r __ksymtab_preempt_notifier_register >>>>> c045ed3c r __kcrctab_preempt_notifier_unregister >>>>> c045ed40 r __kcrctab_preempt_notifier_register >>>>> c0460612 r __kstrtab_preempt_notifier_unregister >>>>> c046062e r __kstrtab_preempt_notifier_register >>>>> c0477824 D preempt_mark_thresh >>>>> f8fc8a68 d kvm_preempt_ops [kvm] >>>>> c0121550 u preempt_notifier_register [kvm] >>>>> c0121580 u preempt_notifier_unregister [kvm] >>>>> f8d46000 t lp_preempt [lp] >>>>> vinitd@pe-lt271:~$ >>>>> >>>>> >>>>> 2) Vanilla kernel (CONFIG_PREEMPT) >>>>> >>>>> # cat /proc/kallsyms | grep preempt >>>>> c00258f4 t svc_preempt >>>>> c00407a8 t check_preempt_curr_rt >>>>> c00407d4 t check_preempt_curr_idle >>>>> c0040ce0 T sub_preempt_count >>>>> c0040d8c T add_preempt_count >>>>> c00441b8 t check_preempt_wakeup >>>>> c0308c84 T preempt_schedule_irq >>>>> c0308d00 T preempt_schedule >>>>> c03b3a70 r __ksymtab_add_preempt_count >>>>> c03b3a78 r __ksymtab_sub_preempt_count >>>>> c03b3a88 r __ksymtab_preempt_schedule >>>>> c03ba5c7 r __kstrtab_add_preempt_count >>>>> c03ba5d9 r __kstrtab_sub_preempt_count >>>>> c03ba5f4 r __kstrtab_preempt_schedule >>>>> # >>>>> >>>>> >>>>> Hope this will help you. >>>>> >>>>> -Vinit >>>>> >>>> >>>> CONFIG_PREEMPT is universal. >>>> >>>> If you look at the definition of preemptible(), it will be clear. >>>> >>>> -Leo. >>>> >>> >>> What do you mean by universal? Do you mean always TRUE? >>> >>> -Vinit >>> >> >> You can read about CONFIG_PREEMPT_VOLUNTARY at, >> >> http://kernel.xc.net/html/linux-2.6.18/i386/PREEMPT_VOLUNTARY >> http://kerneltrap.org/node/3440 >> >> -Vinit >> > > > By universal I meant, CONFIG_PREEMPT should be available on vanilla > kernel as well as Ubuntu kernels. > > If you look here, > http://lxr.linux.no/linux+*/include/linux/hardirq.h#L114 > > you will see that config_preempt is part of vanilla kernel too. If it is not set > then preemptible() will be 0x0, means your kernel is not preemptible. > > -Leo. > You are right, CONFIG_PREEMPT and CONFIG_PREEMPT_VOLUNTARY both are available in vanilla kernel. But its distribution specific decision not to enable CONFIG_PREEMPT in their kernel package. Its really interesting to read the difference between these 2 flags. CONFIG_PREEMPT_VOLUNTARY is also preempting the kernel but not as much as CONFIG_PREEMPT. The possible reason for not enabling CONFIG_PREEMPT can be found here, http://lists.mandriva.com/kernel-discuss/2009-02/msg00027.php http://thread.gmane.org/gmane.comp.audio.pulseaudio.general/2845 -Vinit -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
