On Sun, Mar 12, 2006 at 11:23:17AM +0800, James Yu wrote:
> Hi folks,
>
> I am modifying linux-2.4.18 for ARM (based on S3C2410), I enable only
> the timer interrupt and disable all the others in "init" thread before
> "execve("/sbin/init",argv_init,envp_init);" is taking place.
> I also create two kernel threads by invoking "kernel_thread" right
> after disbling the interrupts. This is how the kernel thread looks
> like:
>
> 923 void eos_1(void)
> - 924 {
> | 925 DECLARE_WAITQUEUE(wait, current);
> | 926
> | 927 while (1)
> |- 928 {
> || 929 printk("\n%s[%d], period:%d, deadline:%d, jiffies:%d.\n",
> || 930 current->comm, current->pid,
> current->period, current->deadline, jiffies);
> || 931 eos_tail();
> || 932 }
> | 933 }
>
> 905 #define eos_tail() \
> - 906 do { \
> | 907 static int deadline = 0; \
> | 908 if ((current->deadline - jiffies) > 0) \
> |- 909 { \
> || 910 deadline = current->deadline; \
> || 911 current->deadline = deadline + current->period; \
> || 912 sleep_on_timeout(&wait, (deadline - jiffies)); \
> || 913 } \
> | 914 else \
> |- 915 { \
> || 916 printk("\n!!! %s[%d] missed deadline !!!\n",
> current->comm, current->pid); \
> || 917 return (0); \
> || 918 } \
> | 919 } while(0)
>
> Now I am trying to modify the "schedule" function. I insert the
> following segment into schedule function after the part that
> re-calculate counters --> if(unlikely(!c)).
>
> |- 634 {
> || 635 int latch = 0;
> || 636
> || 637 list_for_each(tmp, &runqueue_head)
> ||- 638 {
> ||| 639 //p = list_entry(tmp, struct task_struct, run_list);
> ||| 640 latch = latch + 1;
> ||| 641 }
> || 642 printk("{%d}", latch);
> || 643 }
>
> This is where weird thing happens! If I uncomment line 639, kernel
> complains that I am passing an illegal value into "sleep_on_timeout",
> which is called in my kernel thread inside "eos_tail". I copy both
> line 637 and 639 from schedule itself (they were used to pick next job
> to run).
>
> I am simply doing copy & paste inside "schedule", can someone please
> tell me what is happening ?
It might be a wrong gcc optimization which generates bad code. If you're
working on such an old kernel (about 5 years old), maybe you're using
and old, broken compiler too ? gcc-2.95[.1], gcc-2.96, 3.0 and 3.1 have
been known to produce bad code for a long time. Also ensure that you
pass the "-fno-strength-reduce" option to gcc.
Anyway, if you're starting a new dev, I would suggest using a more
recent kernel : 2.6.1[56] or 2.4.32 if you need 2.4.
> Thanks a lot,
> --
> James
> [email protected]
regards,
Willy
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