Dear Robert P. J. Day,
Someone makes a test program like this:
jiffier.c
int main()
{
unsigned long jiffiers = 777;
jiffiers++;
return 0;
}
#gcc -S jiffer1.c (compile it to assembly language)
.file "jiffier1.c"
.version "01.01"
gcc2_compiled.:
.text
.align 4
.globl main
.type main,@function
main:
pushl %ebp
movl %esp, %ebp
subl , %esp
movl 7, -4(%ebp)
leal -4(%ebp), %eax
incl (%eax)
movl , %eax
leave
ret
.Lfe1:
.size main,.Lfe1-main
.ident "GCC: (GNU) 2.96 20000731 (Red Hat Linux 7.3 2.96-110)"
We can see that the value of jiffiers increment directly in the memory.
Sincerely yours,
chiachen
[email protected]
2009-12-30
======= 2009-12-29 22:15, your message: access to jiffies_64 atomic or
not?=======
from kernel/timer.c:
/*
* The 64-bit jiffies value is not atomic - you MUST NOT read it
* without sampling the sequence number in xtime_lock.
* jiffies is defined in the linker script...
*/
void do_timer(unsigned long ticks)
{
jiffies_64 += ticks;
update_wall_time();
calc_global_load();
}
i'm not sure how to interpret that comment since it clearly suggests
that you can't simply access jiffies_64, but that's exactly what
do_timer() is doing in that first line by incrementing it by a certain
value. can anyone clarify whether the above makes any sense?
rday
--
========================================================================
Robert P. J. Day Waterloo, Ontario, CANADA
Linux Consulting, Training and Kernel Pedantry.
Web page: http://crashcourse.ca
Twitter: http://twitter.com/rpjday
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