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. -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
