Re: high load with usb device

[Michael Tokarev <mjt@tls.msk.ru>]

14.09.2010 14:39, Avi Kivity wrote:
>  On 09/14/2010 12:25 PM, Michael Tokarev wrote:
>> Not that it is much helpful either.  lsof:
>>
>> qemu-syst 23203  mjt    0u   CHR   136,9      0t0      12 /dev/pts/9
>> qemu-syst 23203  mjt    1u   CHR   136,9      0t0      12 /dev/pts/9
>> qemu-syst 23203  mjt    2u   CHR   136,9      0t0      12 /dev/pts/9
>> qemu-syst 23203  mjt    3u   CHR  10,232      0t0    4402 /dev/kvm
>> qemu-syst 23203  mjt    4u  0000     0,9        0     607 anon_inode
>> qemu-syst 23203  mjt    5r  FIFO     0,8      0t0 8172675 pipe
>> qemu-syst 23203  mjt    6w  FIFO     0,8      0t0 8172675 pipe
>> qemu-syst 23203  mjt    7u   CHR  10,200      0t0    1228 /dev/net/tun
>> qemu-syst 23203  mjt    8u  0000     0,9        0     607 anon_inode
>> qemu-syst 23203  mjt    9u  IPv4 8173217      0t0     TCP *:5900 (LISTEN)
>> qemu-syst 23203  mjt   10u  0000     0,9        0     607 anon_inode
>> qemu-syst 23203  mjt   11u  0000     0,9        0     607 anon_inode
>> qemu-syst 23203  mjt   12u  0000     0,9        0     607 anon_inode
> 
>> So it is constantly poking fds# 11, 12, 10, 5&  6.
>> 5 and 6 are pipe (selfpipe?),
> 
> signalfd emulation, used to deliver signals efficiently.  Older glibc?

[e]glibc-2.11.

$ grep SIGNAL config-host.mak
CONFIG_SIGNALFD=y

>From strace of another run:
24318 signalfd(-1, [BUS ALRM IO], 8)    = 12
(so one of the remaining fds is a signalfd :)

>> and 10..12 are "anon inode".
> 
> Those are likely eventfds.
> 
>> Here's the command line again:
>>
>> qemu-system-x86_64 \
>>    -netdev type=tap,ifname=tap-kvm,id=x \
>>    -device virtio-net-pci,netdev=x \
>>    -monitor stdio \
>>    -boot n \
>>    -usbdevice tablet \
>>    -m 1G \
>>    -vnc :0
>>
>> Yes, it does quite a lot of timer stuff... ;)
> 
> So timers internal to usb.
> 
> Please try (independently):
> 
> - just -usb, without -usbdevice tablet

No, that one works as expected - all quiet.
-usbdevice tablet is also quiet up until
guest loads usb host controller driver
(not particular usb device driver).

> - instrument calls to qemu_mod_timer() in hw/usb-*hci.c.  Looks like
> these are all 1kHz, but something else is clearly happening.

Doing that now...

Thanks!

/mjt