My laptop was struggling to play youtube videos this morning so I took
a peek in top and noticed the watchdog/1 thread hogging my CPU. Next
step I take a peek with perf:
49.57% kworker/1:1 [kernel.kallsyms] [k] native_read_tsc
|
--- native_read_tsc
|
|--92.49%-- delay_tsc
| __const_udelay
| e1000_acquire_swflag_ich8lan
| e1000e_read_phy_reg_igp
| e1000e_phy_has_link_generic
| e1000_check_for_copper_link_ich8lan
| e1000e_has_link
| e1000_watchdog_task
| process_one_work
| worker_thread
| kthread
| ret_from_fork
Alright, so we're callingn udelay from e1000_acquire_swflag_ich8lan.
How often and for how long? I take a look with trace-cmd:
kworker/1:2-23734 [001] 3971.629095: funcgraph_entry: |
e1000_acquire_swflag_ich8lan() {
kworker/1:2-23734 [001] 3971.629098: funcgraph_entry: ! 999.674 us |
delay_tsc();
kworker/1:2-23734 [001] 3971.630100: funcgraph_entry: ! 999.639 us |
delay_tsc();
kworker/1:2-23734 [001] 3971.631101: funcgraph_entry: ! 999.639 us |
delay_tsc();
<snip>...<snip>
kworker/1:2-23734 [001] 3972.630995: funcgraph_exit: ! 1001899 us | }
So I see it calls mdelay(1) over and over again for a total of 1
second. Looks like I'm getting stuck in this bit of code where
SW_FLAG_TIMEOUT is 1 second:
timeout = SW_FLAG_TIMEOUT;
extcnf_ctrl |= E1000_EXTCNF_CTRL_SWFLAG;
ew32(EXTCNF_CTRL, extcnf_ctrl);
while (timeout) {
extcnf_ctrl = er32(EXTCNF_CTRL);
if (extcnf_ctrl & E1000_EXTCNF_CTRL_SWFLAG)
break;
mdelay(1);
timeout--;
}
I guess I have two questions:
1) Do these need to be mdelays instead of msleeps? It looks like in
my case this is called from process context, but I didn't audit all of
the callers of this function and maybe it can happen from interrupt
context too?
2) Any idea why I'm hitting this in the first place?
$ lspci | grep Ether
00:19.0 Ethernet controller: Intel Corporation 82566MM Gigabit Network
Connection (rev 03)
$ ethtool -i eth0
driver: e1000e
version: 2.2.14-k
firmware-version: 0.3-0
bus-info: 0000:00:19.0
supports-statistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
supports-priv-flags: no
$ uname -r
3.9.3-201.fc18.x86_64
Thanks,
Shawn
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