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