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SubjectRe: ksoftirqd uses 99% CPU triggered by network traffic (maybe RLT-8139 related)
On Sun, 25 Jul 2004, Francois Romieu wrote:

> Pasi Sjoholm <ptsjohol@cc.jyu.fi> :
> [...]
> > I haven't been able to reproduce this with normal www-browsing or
> > ssh-connections but it's always reproducible when my eth0 is under heavy
> > load.
> I guess it can be reproduced even if the binary (nvidia ?) module is never
> loaded after boot, right ?

After 24 hours of hard working I can answer yes to this question.
Now I can reproduce this from 2 to 15 minutes with 2 cp-processes from
samba->workstation->nfs, some software building with make -j 3, playing
some mp3 via nfs to notice when kernel goes down.. =) and so on..

After that ksoftirqd takes almost all the cpu-time and the network is not
working at all.

First I made some debugging with:

--
readprofile -r
sleep 10
readprofile -n -v -m /boot/System.map-2.6.7-mm7| sort -n +2 | tail -40
--

I tried this tree different times and here are the results:

-1-
c0114020 unshare_files 1 0.0104
c0134400 vma_prio_tree_add 1 0.0057
c01f1c50 fast_clear_page 1 0.0104
c01f2190 __copy_to_user_ll 7 0.0625
c017dbf0 write_profile 9 0.1406
c02d1f50 net_rx_action 10 0.0368
00000000 total 29 0.0000
-1-

-2-
c0111c80 finish_task_switch 1 0.0069
c011f9e0 get_signal_to_deliver 1 0.0012
c01364c0 __kmalloc 1 0.0078
c013ad60 copy_page_range 1 0.0017
c0141370 page_remove_rmap 1 0.0069
c014a9f0 do_sync_write 1 0.0057
c014aaa0 vfs_write 1 0.0033
c0195840 start_this_handle 1 0.0010
c01f1c20 add_timer_randomness 1 0.0035
c023f4e0 idedisk_release 1 0.0052
c017dbf0 write_profile 5 0.0781
c01f1f30 extract_entropy 5 0.0060
c02d1f90 rt_may_expire 14 0.0972
00000000 total 34 0.0000
-2-

-3-
c01105b0 do_page_fault 1 0.0007
c012d920 find_lock_page 1 0.0045
c0131130 bad_page 1 0.0063
c01ec430 slow_copy_page 1 0.0208
c01ec2f0 fast_copy_page 3 0.0117
c017dcf0 kclist_add 4 0.0625
c01ec900 copy_from_user 4 0.0312
c02c5f00 dev_ifname 6 0.0341
00000000 total 21 0.0000
-3-

There are quite few ticks in total-rows at least when you are comparing to
normal operation of kernel:

--
c017dcf0 kclist_add 9 0.1406
c0119100 __do_softirq 268 2.0938
c0101eb0 default_idle 9396 195.7500
00000000 total 9779 0.0043
--

Also made some debugging with patch which Andrew Morton gave to brad
(http://seclists.org/lists/linux-kernel/2004/Mar/2295.html)

--cut--
diff -puN include/linux/kernel.h~proc-sys-debug include/linux/kernel.h
--- 25/include/linux/kernel.h~proc-sys-debug 2004-02-25 23:12:56.000000000
-0800+++ 25-akpm/include/linux/kernel.h 2004-02-25 23:12:57.000000000
-0800
@@ -214,6 +214,8 @@ extern void dump_stack(void);
1; \
})

+extern int proc_sys_debug[8];
+
#endif /* __KERNEL__ */

#define SI_LOAD_SHIFT 16
diff -puN -L kernel/ksyms.c /dev/null /dev/null
diff -puN kernel/sysctl.c~proc-sys-debug kernel/sysctl.c
--- 25/kernel/sysctl.c~proc-sys-debug 2004-02-25 23:12:56.000000000 -0800
+++ 25-akpm/kernel/sysctl.c 2004-02-25 23:21:37.000000000 -0800
@@ -849,7 +849,26 @@ static ctl_table fs_table[] = {
{ .ctl_name = 0 }
};

+int proc_sys_debug[8];
+EXPORT_SYMBOL(proc_sys_debug);
+
static ctl_table debug_table[] = {
+ {1, "0", &proc_sys_debug[0], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
+ {2, "1", &proc_sys_debug[1], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
+ {3, "2", &proc_sys_debug[2], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
+ {4, "3", &proc_sys_debug[3], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
+ {5, "4", &proc_sys_debug[4], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
+ {6, "5", &proc_sys_debug[5], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
+ {7, "6", &proc_sys_debug[6], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
+ {8, "7", &proc_sys_debug[7], sizeof(int), 0644, NULL,
+ &proc_dointvec_minmax, &sysctl_intvec, NULL, NULL, NULL},
{ .ctl_name = 0 }
};

_
kernel/softirq.c | 7 ++++++-
1 files changed, 6 insertions(+), 1 deletion(-)
diff -puN kernel/softirq.c~a kernel/softirq.c
--- 25/kernel/softirq.c~a 2004-03-11 02:05:20.000000000 -0800
+++ 25-akpm/kernel/softirq.c 2004-03-11 02:06:02.000000000 -0800
@@ -54,8 +54,13 @@ static inline void wakeup_softirqd(void)
/* Interrupts are disabled: no need to stop preemption */
struct task_struct *tsk = __get_cpu_var(ksoftirqd);

- if (tsk && tsk->state != TASK_RUNNING)
+ if (tsk && tsk->state != TASK_RUNNING) {
+ if (proc_sys_debug[0]) {
+ printk("%s wakes ksoftirqd\n", current->comm);
+ dump_stack();
+ }
wake_up_process(tsk);
+ }
}
--cut--

and running:
dmesg -c
echo 1 > /proc/sys/debug/0 ; sleep 5; echo 0 > /proc/sys/debug/0
dmesg -s 1000000 > /tmp/foo
but it resulted nothing in /tmp/foo and ksoftirqd was eating my cpu time.

SysRq: Show regs gave this:

--
Pid: 2, comm: ksoftirqd/0
EIP: 0060:[<e0871224>] CPU: 0
EIP is at rtl8139_poll+0xb4/0x100 [8139too]
EFLAGS: 00000247 Not tainted (2.6.7-mm7)
EAX: ffffe000 EBX: 00000040 ECX: df4824f8 EDX: c0441978
ESI: df482400 EDI: e0868000 EBP: dff85f80 DS: 007b ES: 007b
CR0: 8005003b CR2: b7c5a000 CR3: 1fafd000 CR4: 000006d0
[<c0119580>] ksoftirqd+0x0/0xc0
[<c02c5f3a>] net_rx_action+0x6a/0x110
[<c01191a9>] __do_softirq+0xa9/0xb0
[<c01191d7>] do_softirq+0x27/0x30
[<c01195e8>] ksoftirqd+0x68/0xc0
[<c01277e5>] kthread+0xa5/0xb0
[<c0127740>] kthread+0x0/0xb0
[<c0102111>] kernel_thread_helper+0x5/0x14
--
I'm not a kernel expert but it would seem that ksoftirqd is in some sort a
loop because I didn't get any "printk("%s wakes ksoftirqd\n",
current->comm);"-lines.

And rtl8139_poll-function in rtl-8139-drivers is a function made directly
for NAPI's poll(). But for me is hard to say what's wrong... I will try
other 8139-card later today if it has a same problem.

> [...]
> > Same thing for me also, except for me it's interrupt 10 (CMI8738-MC6,
> > eth0), so it's pointing more and more something rtl-8139 related.
> Possible. Which 8139 module do you use ?

8139too.

> It would be nice if this thread could be fed to netdev@oss.sgi.com.

Included in cc.

I haven't changed anything else in my hardware but just upgraded my
10Mbps hub to 100Mbps switch. I guess 10Mbps wasn't generating too many
interrupts. =)

Hope this helps..

--
Pasi Sjöholm

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