poking around under /proc on my quad-core asus laptop and just
noticed that while /proc/cpuinfo (properly) lists my 8 processors,
/proc/softirqs instead lists 16, with the last 8 having values of all
zeroes (not surprisingly). with the middle columns snipped for
brevity, my /proc/softirqs shows:
CPU0 CPU1 ... CPU13 CPU14 CPU15
HI: 0 0 ... 0 0 0
TIMER: 1018887 45313 ... 0 0 0
NET_TX: 1182 1813 ... 0 0 0
NET_RX: 991 719 ... 0 0 0
BLOCK: 44559 13 ... 0 0 0
BLOCK_IOPOLL: 0 0 ... 0 0 0
TASKLET: 41582 419 ... 0 0 0
SCHED: 76438 28658 ... 0 0 0
HRTIMER: 738 709 ... 0 0 0
RCU: 136797 82392 ... 0 0 0
with all of the zero values from CPU8-CPU15. so the obvious question
is -- why? why the difference in the way those two proc files count
the "number" of CPUs on my system?
for /proc/cpuinfo, the logic is in arch/x86/kernel/cpu/proc.c, and
the way the seq_file is implemented:
static void *c_start(struct seq_file *m, loff_t *pos)
{
*pos = cpumask_next(*pos - 1, cpu_online_mask);
if ((*pos) < nr_cpu_ids)
return &cpu_data(*pos);
return NULL;
}
so that loop clearly iterates through the "online" CPUs, which would
appear to be the correct loop criteria.
the code for softirqs, however, is in fs/proc/softirqs.c, and is
much simpler:
static int show_softirqs(struct seq_file *p, void *v)
{
int i, j;
seq_puts(p, " ");
for_each_possible_cpu(i)
seq_printf(p, "CPU%-8d", i);
seq_putc(p, '\n');
for (i = 0; i < NR_SOFTIRQS; i++) {
seq_printf(p, "%12s:", softirq_to_name[i]);
for_each_possible_cpu(j)
seq_printf(p, " %10u", kstat_softirqs_cpu(i, j));
seq_putc(p, '\n');
}
return 0;
}
note that that code uses the macro "for_each_possible_cpu()" rather
than examining only *online* CPUs. in dmesg, i see the lines:
[ 0.000000] smpboot: Allowing 16 CPUs, 8 hotplug CPUs
[ 0.000000] setup_percpu: NR_CPUS:256 nr_cpumask_bits:256 nr_cpu_ids:16 nr_node_ids:1
and the code for all this counting is in arch/x86/kernel/smpboot.c,
which you can check out for yourself, but this brings me back to the
basic question -- why is the code for softirqs iterating through all
*possible* CPUs (in my case, apparently, 16), when i have only 8
*online* CPUs?
rday
--
========================================================================
Robert P. J. Day Ottawa, Ontario, CANADA
http://crashcourse.ca
Twitter: http://twitter.com/rpjday
LinkedIn: http://ca.linkedin.com/in/rpjday
========================================================================
_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
