14.09.2010 17:25, Avi Kivity wrote:
> On 09/14/2010 03:15 PM, Michael Tokarev wrote:
[]
>> Looking at what hw/usb-uhci.c:uhci_frame_timer() routine
>> does, it is quite expected to have that many writes and
>> reads and that many gettimers(). It is polling for events
>> every 1/1000th of a second, instead of using some form of
>> select().
>
> IIUC that's mandated by USB hardware. The guest may place data in
> memory, and USB polls it to see if it needs to tell send some message on
> the bus.
Well, checking guest memory does not involve so many
reads/writes, i guess ;)
> Please post an strace again, this time with -e trace=select. Looks like
> each timer callback results in>50 syscalls, 4 of which are select()s).
Here we go.
qemu-syst 25728 mjt 0u CHR 136,9 0t0 12 /dev/pts/9
qemu-syst 25728 mjt 1u CHR 136,9 0t0 12 /dev/pts/9
qemu-syst 25728 mjt 2u CHR 136,9 0t0 12 /dev/pts/9
qemu-syst 25728 mjt 3u CHR 10,232 0t0 4402 /dev/kvm
qemu-syst 25728 mjt 4u 0000 0,9 0 607 anon_inode
qemu-syst 25728 mjt 5r FIFO 0,8 0t0 11703862 pipe
qemu-syst 25728 mjt 6w FIFO 0,8 0t0 11703862 pipe
qemu-syst 25728 mjt 7u CHR 10,200 0t0 1228 /dev/net/tun
qemu-syst 25728 mjt 8u 0000 0,9 0 607 anon_inode
qemu-syst 25728 mjt 9u IPv4 11704055 0t0 TCP *:5900 (LISTEN)
qemu-syst 25728 mjt 10u 0000 0,9 0 607 anon_inode
qemu-syst 25728 mjt 11u 0000 0,9 0 607 anon_inode
qemu-syst 25728 mjt 12u 0000 0,9 0 607 anon_inode
17:27:23.995096 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 1 (in [12], left {0, 998573})<0.001461>
17:27:23.996994 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 2 (in [5 10], left {0, 999987})<0.000042>
17:27:23.997258 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 1 (in [12], left {0, 999998})<0.000011>
17:27:23.997561 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 2 (in [5 10], left {0, 999998})<0.000009>
17:27:23.997739 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 1 (in [12], left {0, 998771})<0.001256>
17:27:23.999458 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 2 (in [5 10], left {0, 999991})<0.000017>
17:27:23.999665 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 1 (in [12], left {0, 999998})<0.000010>
17:27:23.999996 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 2 (in [5 10], left {0, 999998})<0.000009>
17:27:24.000199 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 1 (in [12], left {0, 998775})<0.001241>
17:27:24.001666 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 2 (in [5 10], left {0, 999997})<0.000006>
17:27:24.001768 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 1 (in [12], left {0, 999932})<0.000103>
17:27:24.001985 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 2 (in [5 10], left {0, 999998})<0.000005>
17:27:24.002061 select(13, [0 5 7 9 10 12], [], [], {1, 0}) = 1 (in [12], left {0, 998407})<0.001617>
